UNIVERSITY  FARM 


A  MANUAL 

OF 

NORMAL  HISTOLOGY 

AND 

ORGANOGRAPHY 


BY 
CHARLES  HILL,  B.  S.,  M.  S.,  PH.D.,  M.  D. 

PRESIDENT  AND  PROFESSOR  OF   ANATOMY,  CHICAGO  HOSPITAL  COLLEGE  OF  MEDI- 
CINE;    PROFESSOR    OF    HISTOLOGY    AND    EMBRYOLOGY,    CHICAGO    VETERI- 
NARY  COLLEGE;    FORMERLY   ASSISTANT  PROFESSOR  OF  HISTOLOGY 

AND      EMBRYOLOGY      AT      THE      NORTHWESTERN     UNIVERSITY 
MEDICAL    SCHOOL,   CHICAGO 


Fourth  Edition,   Thoroughly  Revised 


PHILADELPHIA   AND    LONDON 

W.    B.    SAUNDERS    COMPANY 
mo 


UNIVERSITY  OF  CALIFORNIA 

LIBRARY 

BRANCH  OF  THE 
COLLEGE  OF  AGRICULTURE 


Copyright,  1906,  by  W.  B.  Saunders  Company.   Revised,  reprinted,  and 

recopyrighted  January,   1909.     Reprinted   September,  1910. 

Revised,  reprinted,  and  recopyrighted   July,    1914. 

Reprinted     September,     1915.     Revised, 

reprinted,  and  recopyrighted 

September,  1917 


Copyright,  1917,  by  W.  B.  Saunders  Company 


Reprinted  May,  1920 


PRINTED    IN    AMERICA 


PRESS    OF 

W.    B.    SAUNDERS    COMPANY 
PHILADELPHIA 


PREFACE  TO  FOURTH  EDITION. 


THE;  cordial  reception  given  this  text  is  much 
appreciated  by  both  the  author  and  the  publishers. 
In  issuing  a  fourth  edition  the  chapters  have  again 
been  carefully  reviewed  and  the  known  facts  to  date 
in  elementary  histology  have  been  properly  recorded. 

The  new  introduction  is  written  wholly  for  the 
elementary  student,  to  arouse  in  him  an  interest  in 
the  subject  matter  of  the  text,  and  to  show  the  close 
relation  of  normal  histology  to  kindred  important 
sciences.  The  text  on  spermatogenesis  has  been 
enlarged  and  the  known  facts  stated  in  as  clear  and 
brief  a  manner  as  possible.  Some  of  the  figures 
have  been  replaced  with  new  ones,  and  minor 
changes  have  been  introduced  throughout  the  text 
wherever  the  subject  matter  could  be  improved. 

In  this,  as  well  as  in  former  editions,  the  author 
has  kept  in  mind  his  original  fundamental  purpose, 
to  issue  a  clear  and  concise  text  that  could  be  used 
as  a  basis  on  which  the  instructor  might  "  build 
and  complete  his  ideal  elementary  course  in  his- 
tology." 

_  CHARLES  Hiu<. 

CHICAGO,  lu,.. 


PREFACE 


THIS  manual  is  written  in  the  interest  of  element- 
ary students.  The  fundamental  facts  in  histology 
have  therefore  been  presented  in  as  clear  and 
concise  a  manner  as  possible,  and  theories  advanced 
only  to  simplify  the  facts  and  aid  the  memory  in 
their  retention.  The  figures  have  been  selected 
with  considerable  care  and  are  intended  to  illus- 
trate the  salient  points  of  the  text.  They  are  to 
be  studied  as  critically  as  the  text,  and  to  further 
facilitate  such  a  study  the  descriptive  terms  are 
placed  on  the  figures  rather  than  in  foot-notes. 

The  oral  cavity  deserves  more  attention  than 
is  usually  given  this  subject.  Neglect  of  proper 
care  of  teeth  is  a  common  failing,  and  the  cause 
may  be  traced  directly  to  a  lack  of  knowledge 
of  their  structure  and  function.  This  chapter  has 
therefore  been  enlarged.  The  author  is  greatly 
indebted  to  Professor  Frederick  B.  Noyes,  of  the 
Northwestern  University  Dental  School,  for  con- 
tributing most  excellent  figures  on  this  subject. 
His  critical  essays  form  the  basis  for  the  descriptive 
part  of  this  chapter. 

The  author  believes  most  thoroughly  in  the 
laboratory  method  of  study.  He  believes,  too, 
that  the  laboratory  work  should  precede  the  class- 

ii 


12  PREFACE. 

room  work,  for  which  this  manual  is  written. 
Laboratory  technique,  however,  is  so  extensive  a* 
subject  that  a  laboratory  text,  or  the  teacher's 
personal  outlines,  should  be  used  for  this  particular 
work.  In  conformity  with  this  view,  only  the  funda- 
mental principles  of  laboratory  technique  are  out- 
lined in  the  text. 

Lastly,  the  subjects  treated  have  been  made  funda- 
mental and  brief,  that  the  teacher  in  charge  may 
supplement  the  chapters  by  collateral  work  as  may 
fit  the  particular  course  offered.  It  is  therefore  a 
basis  on  which  the  instructor  may  build  and  com- 
plete his  ideal  elementary  course  in  histology. 

CHARLES  HILU 


CONTENTS. 


PAGE. 

INTRODUCTION ,,..,., 17 

Protoplasm 7.7 

CHAPTER  I. 

DEVELOPMENT 26 

The  Cell 34 

CHAPTER  II. 

TISSUES , 49 

Epithelial  Tissue 49 

Supporting  Tissue 64 

Connective  Tissue 66 

Cartilage 74 

Bone 77 

Muscular  Tissue 85 

Nervous  Tissue 94 

CHAPTER  III. 

CIRCULATORY  SYSTEM,  BLOOD,  MARROW,  AND  LYMPHATIC  ORGANS  108 

Heart 108 

Arteries  and  Veins 109 

Blood 1 16 

Marrow 121 

Lymphatic  System 125 

Thymus  Gland 129 

Spleen 132 

CHAPTER  IV 

DIGESTIVE  SYSTEM 136 

Mouth . . . .' 136 

Teeth „ 143 

Tongue. . .  0 172 

Pharynx 180 

Esophagus : 182 

Stomach 184 

Small  Intestine 194 

Large  Intestine 200 


14  CONTENTS. 

PAGE 
CHAPTER  V. 

DIGESTIVE  GLANDS 207 

Salivary  Glands 207 

Pancreas 212 

Liver 216 

CHAPTER  VI. 

ORGANS  OF  RESPIRATION ; ...  231 

Larynx 231 

Thyroid  Gland , 235 

Parathyroids 238 

Trachea  and   Bronchi 239 

Lung 242 

CHAPTER  VII. 

THE  URINARY  ORGANS 253 

Suprarenal  Glands 253 

Kidneys 257 

Ureters 269 

Urinary  Bladder 271 

CHAPTER  VIII. 

REPRODUCTIVE  ORGANS  IN  MALE 275 

Testicles 275 

Penis 289 

Prostate  Gland 297 

CHAPTER  IX. 

REPRODUCTIVE  ORGANS  IN  THE  FEMALE 301 

Ovaries 301 

Fallopian  Tubes 313 

Uterus 317 

Pregnancy 327 

Mammary  Gland 332 

CHAPTER  X. 

THE  SKIN 337 

Hairs 343 

Nails 349 

Glands  of  skin ,  356 


CONTENTS.  15 

CHAPTER  XI. 

PERIPHERAL  NERVE  TERMINATIONS 361 

^Motor  Nerve  Endings 361 

Sensory  Nerve  Endings 363 

CHAPTER  XII. 

SPINAL  CORD •.  37I 

CHAPTER  XIII. 

THE  BRAIN 384 

Medulla ^35 

Summary  of  Tracts,  their  Origin  and  Terminations 394 

Pons 394 

Cerebellum 398 

Cerebral  Cortex 403 

Neuroglia 406 

Blood-vessels  of  Central  Nervous  System 409 

CHAPTER  XIV. 

THE  EYE 41 1 

Tunica  Externa 414 

Tunica  Media 418 

Tunica  Interna 42 1 

Refracting  Media 428 

Blood-vessels 430 

CHAPTER  XV. 

ORGAN  OP  HEARING 437 

Development  of  Labyrinth 45 1 

CHAPTER  XVI. 

OLFACTORY  ORGAN 453 

CHAPTER  XVII. 

LABORATORY  DIRECTIONS 456 

Preparation  of  Material 456 

Preparation  of  Elastic  Fibers 466 

Standard  Fixing  Solutions , .  472 

Standard  Stains 475 


INDEX .,.,.,  479 


A  MANUAL  OF 

NORMAL   HISTOLOGY 

AND 

ORGANOGRAPHY. 


INTRODUCTION. 
PROTOPLASM. 

IN  all  this  material  world,  with  its  complexity 
of  products,  there  are  but  two  forms  of  material 
things — namely,  living  matter  or  protoplasm  and 
lifeless  or  dead  matter.  Protoplasm  is  not  life.  We 
do  not  know  what  life  is,  but  whatever  it  is,  we 
know  it  is  not  a  material  substance.  We  cannot 
see,  feel,  taste,  touch,  or  weigh  life,  but  we  can  do 
all  these  things  with  protoplasm.  Spencer  defines 
life  as  the  "continuous  adjustment  of  internal  rela- 
tions to  external  relations" — an  acceptable  concept. 

Protoplasm  always  reflects  life,  and  it  is  therefore 
regarded  as  the  physical  basis  of  life.  Protoplasm, 
whether  in  plant  or  in  animal,  shows  a  uniformly 
related  structure  and  has  many  identical  character- 
istics. It  is  a  colorless,  transparent,  jelly-like  sub- 
stance, of  an  albuminoid  nature,  resembling  the 


1 8       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

white  of  an  egg.  It  differs  from  all  lifeless  matter 
in  being  able  to  reproduce  itself,  repair  a  wasted  or 
depleted  condition,  develop,  and  grow.  The  sharpest 
kind  of  a  line  divides  this  living  matter  from  dead 
matter,  and  yet  we  know  that  the  closest  relations 
and  interrelations  do  exist.  Even  in  our  own  phys- 
ical bodies  these  two  forms  prevail,  for  the  outer 
layer  of  the  skin,  the  hair  and  nails,  the  liquid  part 
of  blood  and  lymph,  the  fibers  of  ligaments  and 
tendons,  the  lime  of  bone,  all  are  lifeless  or  dead 
matter.  While  today  we  firmly  believe  that  living 
matter  develops  only  from  pre-existing  living  mat- 
ter, we  know  that  dead  matter  is  constantly  and 
unceasingly  being  incorporated  into  living  matter, 
actually  transformed  into  living  matter  through  the 
mysterious  elaboration  of  this  selfsame  living  sub- 
stance. Thousands  of  tons  of  dead  matter  are  thus 
daily  converted  into  living  matter,  throughout  the 
animal  and  vegetable  kingdoms,  on  land  and  in  the 
seas.  Were  this  constructive  force  nature's  only 
process,  a  most  unfortunate  condition  would  soon 
prevail,  with  a  dearth  of  the  one  form  and  a  great 
surplus  of  the  other — the  living.  But  we  recognize 
a  reverse  current  equally  strong  whereby  the  "dust 
shall  return  to  the  earth  as  it  was  and  the  spirit  to 
the  God  who  gave  it."  That  mysterious  and  in- 
sidious enemy  Death  is  absolutely  necessary  that 
man,  or  any  other  living  being,  may  live.  It  is  the 
duty  of  the  medical  profession  to  divert  this  return 
current  as  far  as  possible  that  humanity,  one  and 
all,  may  enjoy  threescore  and  ten  happy  years. 
Protoplasm,  so  intimately  associated  with  life,  has 


PROTOPLASM.  19 

been  subjected  to  all  forms  of  analyses.  The  chemist 
tells  us  that  protoplasm,  whether  animal  or  plant, 
yields  the  following  elements:  carbon,  hydrogen,  oxy- 
gen, nitrogen,  and  some  sulphur.  He  is  unable  to 
tell  us  the  combining  relation  of  these  elements  in 
protoplasm,  for  the  obvious  reason  that  in  his  anal- 
yses protoplasm  as  living  substance  is  destroyed  and 
life  has  departed.  But  it  is  of  interest  to  know  that 
these  elements,  combined  in  some  mysterious  and 
unknown  way,  make  this  marvelous  substance  liv- 
ing matter.  It  is  also  of  interest  to  reflect  briefly 
upon  the  individual  peculiarities  of  these  elements. 
Carbon  is  a  solid,  exists  free  in  nature,  and  remark- 
able for  its  allotropic  forms,  it  being  found  as  coal, 
or  graphite,  or  diamond.  Its  combining  power  with 
other  elements  is  extensive,  and  its  durability  is 
well  known.  Hydrogen  is  a  gas.  It  is  the  lightest 
known  substance.  It  is  practically  never  found 
free  in  nature.  Its  combinations  with  other  ele- 
ments are  many,  forming  often  very  stable  com- 
pounds, the  most  common  being  its  union  with  oxy- 
gen to  form  water.  Oxygen  is  a  gas  and  found  free 
in  nature,  forming  nearly  20  per  cent,  of  the  atmos- 
phere. Its  combining  power  is  perhaps  the  most 
extensive  of  all  the  elements,  forming  many  stable 
oxides.  Nitrogen  is  also  a  gas  and  found  free  in 
nature,  forming  about  79  per  cent,  of  the  atmosphere. 
Unlike  oxygen,  its  combining  power  with  other  ele- 
ments is  very  weak,  and  when  it  does  so  combine 
the  substances  formed  are  very  unstable.  Nitro- 
gen, therefore,  is  one  of  the  chief  elements  in  our 
explosives.  Sulphur,  like  carbon,  is  remarkable  for 


20       NORMAL   HISTOLOGY  AND    ORGANOGRAPHY. 

its  allotropic  forms.    Very  small  amounts  of  sulphur 
are  found  in  living  matter. 

Protoplasm  is  a  restless  substance,  its  granules 
manifesting  a  slow  ameboid  movement,  which  be- 
comes accelerated  with  increased  physiological  ac- 
tivity. At  the  end  of  a  day's  labor  and  toil  it  is 
not  only  exhausted  but  actually  depleted,  requiring 
repair  and  the  replacing  of  its  lost  particles,  which 
is  accomplished  by  some  marvelous,  subtle,  intrinsic 
power  so  characteristic  of  living  matter.  Food  is 
the  raw  material  utilized  for  this  purpose,  and  it 
naturally  follows  that  the  essential  elements  of  food, 
whether  for  plants  or  animals,  must  be  identical  with 
those  found  in  protoplasm — namely,  carbon,  hydro- 
gen, oxygen,  nitrogen,  and  some  sulphur.  This  is 
universally  the  case,  as  we  find  these  present  in  the 
necessary  food  products,  such  as  carbohydrates,  hy- 
drocarbons, albuminoids,  and  proteins.  As  a  mat- 
ter of  fact,  the  diet  of  man  is  largely  the  protoplasm 
of  some  other  living  organism,  animal  or  vegetable, 
or  both.  Huxley,  in  his  lecture  on  the  "Physical 
Basis  of  Life,"  very  fittingly  outlines  this  transmu- 
tation of  the  elements  of  protoplasm  when  he  says 
that  in  order  to  replace  the  ' '  number  of  grains  of 
protoplasm  and  other  bodily  substances  wasted  in 
maintaining  my  vital  processes  ...  I  shall  prob- 
ably have  recourse  to  the  substance  commonly  called 
mutton  .  .  .  and  the  subtle  influence  to  which  it 
will  then  be  subjected  will  convert  the  dead  proto- 
plasm into  living  protoplasm  and  transubstantiate 
sheep  into  man.  Nor  is  this  all.  If  digestion  were 
a  thing  to  be  trifled  with,  I  might  sup  upon  lobster 


PROTOPLASM.  21 

and  the  matter  of  life  of  the  Crustacea  would  undergo 
the  same  wonderful  metamorphosis  into  humanity. 
And  were  I  to  return  to  my  own  place  by  sea  and 
undergo  shipwreck  the  Crustacea  might  and  prob- 
ably would  return  the  compliment  and  demonstrate 
our  common  nature  by  turning  my  protoplasm  into 
living  lobster." 

The  medical  student  is  here  reminded  of  the  con- 
stant warfare  being  waged  between  many  forms  of 
living  matter.  We  acknowledge  today  that  most 
of  the  diseases  to  which  mankind  is  an  heir  and  a 
victim  are  nothing  else  than  vicious  attacks  upon 
us  by  some  form  of  living  matter.  Tuberculosis, 
pneumonia,  diphtheria,  typhoid,  tetanus,  cholera, 
bubonic  plague,  and  many  other  serious  and  fatal 
diseases  are  now  directly  traced  to  invasions  of  mi- 
cro-organisms, truly  living  things.  Self-preservation 
is  nature's  first  law  and  it  is  God's  law.  Protective 
selfishness  and  the  preservation  of  a  race,  whatever 
be  the  sacrifice,  is  a  fundamental  principle  deeply 
implanted  in  every  form  of  living  organism.  There 
is,  therefore,  no  mercy  shown  in  this  warfare.  There 
is  no  hope  of  peace  in  this  conflict,  nay,  not  even  a 
respite,  and  sooner  or  later  practically  each  one  of 
us  must  fall  a  victim  to  the  enemy's  invasion. 

The  discovery  of  the  germ  origin  of  disease  has 
placed  the  study  of  medicine  on  a  new  and  substantial 
scientific  basis.  Not  satisfied  with  merely  a  defensive 
program,  this  warfare,  by  means  of  preventive  med- 
icine, has  assumed  the  offensive  to  such  a  degree  that 
the  disease  scourges  which  in  the  past  sometimes  de- 
cimated a  people  are  today  an  impossibility. 


22        NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

Histology  is  the  science  that  treats  oi  cells  and 
their  products,  therefore  it  is  largely  a  study  of 
protoplasm.  The  fundamental  principles  of  thera- 
peutics are  based  upon  the  action  of  drugs  on  proto- 
plasm, Pathology  involves  a  recognition  of  micro- 
scopic changes,  other  than  normal,  in  living  matter. 
Physiology  has  much  to  say  about  the  actions  and 
products  of  this  same  substance.  Embryology 
traces  the  developmental  history  of  protoplasm  to 
form  tissues,  organs,  and  a  new  living  being.  It  is 
this  great  importance  of  protoplasm,  and  partic- 
ularly its  relation  to  histology,  that  has  prompted 
these  introductory  remarks. 


CHAPTER  I. 
DEVELOPMENT. 

The  human  body  is  composed  of  related  structural 
units  that  may  be  grouped  in  a  series  of  gradually 
increasing  complexity.  The  simplest  structural  unit 
is  the  cell,  which  is  defined  as  a  spacially  limited 
mass  of  protoplasm  capable  under  certain  conditions 
of  assimilation,  growth,  and  reproduction.  It  is  a 
microscopic  unit  and  forms  the  physical  basis  of  life. 
The  next  grade  of  units  is  a  tissue,  which  consists  of 
a  complex  of  similarly  differentiated  cells  and  their 
derivatives.  Embryonic  tissues  are  mostly  cellular, 
while  in  some  tissues  of  the  adult  body,  such  as  bone 
and  cartilage,  the  cell  products  predominate.  The 
next  higher  grade  of  units  is  an  organ,  which  struc- 
turally consists  of  a  complex  of  tissues  forming  a 
body  with  a  definite  internal  structure  and  external 
form.  Lastly,  the  highest  structural  unit  is  a  system, 
such  as  the  nervous  system,  digestive  system,  respi- 
ratory system,  a  series  of  which,  collectively,  make 
up  the  human  body. 

Histology  is  the  branch  of  science  that  treats  of 
cells  and  their  derivatives.  These  cells,  in  the  adult, 
are  modified  according  to  their  intrinsic  qualities,  en- 
vironment, function,  and  varied  experiences,  which 
enable  us  to  classify  them  and  ultimately  place  them 
in  a  few  elementary  groups. 

The  ovum,  or  starting-point  of  every  individual, 
is  a  cell.  Human  embryology  comprises  its  intra- 

23 


24       NORMAL  HISTOLOGY  AND    ORGANOGRAPHY. 

uterine  development.  Ontogeny  is  a  broader  term, 
which  includes  not  only  embryology,  but  the  develop- 
mental history  of  an  individual  .up  to  old  age  or  the 
senile  condition.  There  is  another  form  of  develop- 
ment, much  slower,  but  just  as  certain  as  ontogeny. 
This  affects  not  only  the  individual,  but,  collectively, 
every  member  of  the  animal  group.  In  the  study  of 
races  there  is  ample  evidence  that  structural  changes 


Fig.  i. —  Formation  of  the  polar  bodies  in  the  ova  of  Asterias  gla- 
cialis  (Hertwig):  ps,  polar  spindle;  pb't  first  polar  body;  pb",  second 
polar  body;  n,  nucleus  returning  to  condition  of  rest. 

have  slowly  but  gradually  taken  place.  This 
broader  developmental  history,  or  history  of  a  race, 
is  known  as  phytogeny.  It  is  closely  interwoven  with 
the  ontogenetic  development,  so  much  so,  that  the 
latter  in  large  part  repeats  the  former,  or  one's 
phylogenetic  history  is  repeated  in  the  ontogeny. 

In  development,  therefore,  the  phylogenetic  or 
intrinsic  qualities  of  a  cell  are  important  factors. 
These  factors  constitute  heredity.  There  is  further 


DEVELOPMENT.  25 

evidence  that  these  factors  are  lodged  in  the  chro« 
matin  of  the  cell  nucleus. 

Environment  is  the  other  great  factor  that  brings 
about  a  structural  modification.  It  is  between 
environment  on  the  one  hand,  and  heredity  on  the 
other,  that  a  specialization  and  differentiation  of 
cells,  tissues,  and  organs  is  produced. 

A  cell  is  a  spacially  limited  mass  of  protoplasm 
which,  under  certain  conditions,  will  assimilate,  grow, 
and  reproduce  itself.  A  tissue  is  a  complex  of  simi- 
larly differentiated  cells  and  their  derivatives.  An 
organ  is  a  complex  of  tissues,  forming  a  body  with  a 
definite  internal  structure  and 
external  form. 


Fig.  2. — Portions  of  the  ova  of  Asterias  glaciah's,  showing  the  ap- 
proach and  fusion  of  the  spermatozoon  with  the  ovum  (Hertwig):  a, 
fertilizing  male  element;  6,  elevation  of  protoplasm  of  egg;  &',  &",  stages 
of  fusion  of  the  head  of  the  spermatozoon  with  the  ovum. 

Ovulation  and  Maturation. — The  ova  develop  in 
the  ovaries  and  are  differentiated  very  early  during 
embryonic  life.  The  estimated  number  of  ova  in  each 
ovary  is  35,000.  It  is  a  remarkable  phenomenon  that 
for  many  years  these  units  show  no  attempt  at  devel- 
opment or  cell  division.  At  the  age  of  puberty  one  or 
more  of  these  cells  pass  periodically  from  the  human 
ovaries,  approximately  every  twenty-eight  days  in  the 


26        NORMAL   HISTOLOGY   AND  ORGANOGRAPHY. 


Malt 

protniilcus. 

Female 

Pronuclciis. 


non-pregnant  woman. 
This  process  is  known 
as     ovulation, 
and  continues 
up  to  the  time 
of  the  meno- 
pause, which  appears 
generally  at  the  age  of 
forty-five. 

As  soon  as  the  ovum 
is  liberated  from  the 
ovary,  a  mitotic  divis- 
ion of  the  nucleus 
takes  place,  and  the 
ovum  extrudes  or  pro- 
duces what  is  called 
the  first  polar  body. 
This  is  a  form  of  bud- 
ding, the  polar  body 
receiving  one-half  the 
original  nucleus  of  the 
ovum.  Without  delay, 
a  second  division  of 
the  nucleus  in  the 
ovum  takes  place,  and 
a  second  polar  body 
is  produced.  This  is 
also  an  equal  division 
of  the  nucleus,  but 
this  time  there  is  a  Fig.  3.— A,  fertilized  ovum  of 

reduction    of    One-half     £*S*  (Hertwig):  the  male  and  the 

female  pronucleus  are  approaching;   in 
the    number    of     chro-     B  they  have  almost  fused;   C,  ovum  of 

mosomes,  and  may  be   ^^^^^ion  of  fertilization 


Segmen- 
tation 
nucleus. 


27 

called  a  reduction  mitosis,  as  distinguished  from  all 
preceding  and  all  succeeding  divisions,  which  are 
called  somatic  mitosis.  The  significance  of  this  re- 
duction has  led  to  many  theories.  During  the 
process  the  nucleus  loses  its  membrane,  is  much  re- 
duced in  size,  and  is  now  known  as  the  female  pro- 
nucleus.  All  these  preliminary  changes  are  known 
as  maturation  of  the  ovum.  Without  fertilization, 
further  development  of  the  ovum  does  not  seem  possi- 
ble in  higher  forms,  and  the  cell  is  invariably  lost. 

Fertilization. — By  this  is  meant  the  union  of  a 
spermatozoon  with  the  ovum,  or,  more  technically, 
the  union  of  a  male  and  a  female  pronucleus.  This 


Fig.  4. —  Diagram  of  the  division  of  the  frog's  egg  (Hertwig): 
Aj  stage  of  the  first  division.  B,  stage  of  the  third  division.  The 
four  segments  of  the  second  stage  of  division  are  beginning  to  be  divi- 
ded by  an  equatorial  furrow  into  eight  segments;  p,  pigmented  surface 
of  the  egg  at  the  animal  pole;  pr,  the  part  of  the  egg  which  is  richer  in 
protoplasm;  d,  the  part  which  is  richer  in  deutoplasm;  sp,  nuclear 
spindle. 

union  takes  place  in  the  upper  part  of  the  oviduct. 
Maturation  always  precedes  fertilization.  But  in 
lower  forms  experiments  upon  unfertilized  eggs  in 
the  absence  of  spermatozoa  have  resulted  in  the 
development  of  embryos,  or  larvae,  and  in  a  few  in- 


28        NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 


stances  adult  animals.  This  interesting  result  may 
be  obtained  by  adding  certain  salts  to  the  sea-water 
in  which  the  eggs  of  marine  animals  normally  de- 
velop, or  in  the  case  of  the  frog  by  puncturing  with 
a  needle  the  outer  layer  of  the  unfertilized  egg. 
Professor  Loeb,  who  inaugurated  these  experiments, 
is  of  the  opinion  that  oxidation  is  thereby  stimu- 
lated, which  is  followed  by  an  accelerated  protoplas- 
mic activity  that  initiates  a  normal  development  of 
these  ova  without  the  process  of  fertilization.  If 
a  spermatozoon  enters  the  ovum  before  the  polar 
bodies  are  extruded,  the  spermatozoon  remains  inert 
within  the  cell  until  maturation  is  completed.  The 
ovum,  thus  reinforced,  enters  upon  an  aggressive 
growth,  a  phenomenon  quite  in  contrast  with  its 
preceding  history. 


Fig.  5. —  Cleavage  in  egg  of  frog,  i  to  16  cell  stage. 

Segmentation  or   Cleavage. — Following  fertiliza- 
tion the  ovum  multiplies  rapidly  by  mitosis.     The 


DEVELOPMENT.  29 

union  of  male  and  female  nuclei  restores  the  reduced 
number  of  chromosomes,  which  remain  constant  and 
usually  even  in  number  for  every  succeeding  division. 
In  certain  insects  an  odd  number  of  chromosomes 
appears,  in  which  case  the  embryo  develops  into  a 
male.  By  repeated  divisions  a  spherical  mass  of 
cells  is  produced,  known  as  the  morula  stage. 


Fig.  6— Blastula  of  triton  taeniatus:   //*,  segmentation  cavity;   rz,  mar- 
ginal zone;  dzt  cells  with  abundant  yolk  (Hertwig). 

Blastula. — The  spherical  mass  quickly  develops 
into  a  hollow  sphere,  lined  by  a  single  layer  of  cells, 
and  is  then  a  blastula.  The  cavity  of  the  blastula 
is  the  segmentation  cavity. 

Gastrula. — A  more  vigorous  growth  seems  to 
take  place  at  one  point  of  the  blastula,  producing 
lateral  pressure  and  an  invagination  at  that  place 
so  as  to  form  a  two-layered  cup-like  structure — in 
some  eggs  a  blastoderm — known  as  the  gastrula .  The 
gastrulae  vary  considerably  according  to  the  different 
forms  of  cleavage.  It  is  an  established  fact  that  all 
metazoa  pass  through  the  morula,  blastula,  and 


30        NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

gastrula  stages,  respectively,  in  the  course  of  their 
development.  The  cup-like  cavity  of  the  gastrula  is 
known  as  the  archenteron  or  codenteron,  and  is  des- 
tined to  develop  into  the  alimentary  canal.  The 
pore  or  external  opening  of  the  coelenteron  is  called 
the  blastopore. 

The  gastrula  has  two  layers  of  cells :  an  outer,  the 
ectoderm,  and  an  inner,  the  entoderm.     The  cells  of 

Segmentation  cavity.  Ectoderm. 


I 

Blaslula.  Blastopore  gaslrula. 

Fig.  7. — Sections  through  a  blastula  and  a  gastrula  of  amphioxus. 

the  entoderm  are  much  larger  than  the  cells  of  the 
ectoderm  and  there  is  thus  a  structural  difference. 
In  cleavage  that  results  in  a  two-layered  blastoderm 
the  term  hypoderm  is  used,  which  is  thus  morpho- 
logically equivalent  to  the  entoderm. 

The  two-layered  gastrula  is  rapidly  invaded  by  a 
third  layer  of  cells,  the  mesoderm,  which  develops 
between  the  first  two  layers  and  ultimately  fills  that 
cavity.  This  cavity,  which  is  the  segmentation 
cavity  of  the  blastula,  permanently  disappears. 
The  origin  of  the  mesoderm  has  long  been  a  con- 
tested question.  The  favored  theory  seems  to  be 
that  for  higher  forms,  at  least,  it  develops  from  the 
hypoderm. 


PLATE  I. 

i,  2,  3,  Diagrams  illustrating  the  segmentation  of  the  mammalian 
ovum  (Allen  Thomson,  after  von  Beneden).  4,  Diagram  illustrating 
the  relation  of  the  primary  layers  of  the  blastoderm,  the  segmentation- 
cavity  of  this  stage  corresponding  with  the  archenteron  of  amphioxus 
(Bonnet). 


Outer  cell. 


PLATE  I. 

Outer  cells 


Inntrcells. 


Inner  cells. 


Inner  cells 


Outer  cells. 


Out* 
cells. 


The  mesoderm,  although  at  first  a  solid  mass  of  cells, 
is  an  invaginated  fold  in  which  a  cavity  soon  appears, 
having  an  inner  layer  of  cells  that  affiliates  closely 


Fig.  8. —  Sagittal  section  through  an  egg  of  triton  (after  the  end  of 
gastrulation) :  ak,  outer  germ-layer;  ik,  inner  germ -layer;  dz,  yolk- 
cells;  dl  and  vl,  dorsal  and  ventral  lips  of  the  coelenteron;  ud,  ccelen- 
teron;  d,  vitelline  plug;  w£,  middle  germ-layer  (Hertwig). 

with  the  hypoderm  cells,  and  an  outer  layer  that  ap- 
plies itself  to  the  ectoderm.  The  hypoderm  with 
its  mesoderm  layer  is  known  as  the  splanchnopleure, 
while  the  ectoderm  and  its  mesoderm  is  the  so- 

Neural  groove.        Somite. 


Enloderm,          Notocord. 
Fig.  9. —  Transverse  section  of  chick  embryo  22  hours  old. 

matopleure.     The  new  cavity  thus  produced  is  the 


32        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

ccelom,  or  body  cavity,  and  is  destined  to  become  the 
pleural  and  peritoneal  cavities.    The  mesoderm  on 


Axial  zone.         /  Neural  canal. 


Somite. 


Lateral  zone. 


Cavity  within  somite. 


Lateral 
plates  for 
gut-tract. 


Vitelline  vein. 
Fig.  10. —  Transverse  section  of  a  sheep  embryo,  17  J  days  (Bonnet). 


Fig.  n. — Rabbit  embryo  of  the  ninth  day,  seen  from  the  dorsal 
side  (after  Kolliker).  The  stem-zone  (stz)  and  the  parietal  zone  (pz) 
are  to  be  distinguished.  In  the  former  8  pairs  of  primitive  segments 
have  been  established  at  the  side  of  the  chorda  and  neural  tube;  ap, 
area  pellucida;  rf,  medullary  groove;  vh,  fore-brain;  ab,  eye-vesicle; 
mh,  mid-brain;  hh,  hind-brain;  uw,  primitive  segment;  stz,  stem-zone; 
pz,  parietal  zone;  h,  heart;  ph,  pericardial  part  of  the  body  cavity;  vd, 
margin  of  the  entrance  to  the  head-gut  (vordere  Darmp}orte\  seen 
through  the  overlying  structures ;  a/,  amniotic  fold  ;  vo,  vena  ompha- 
lomesenterica. 

each  side  of  the  neural  canal  becomes  symmetrically 


DEVELOPMENT. 


33 


blocked  by  means  of  a  longitudinal  fold  and  many 
transverse  folds;  thus  many  segments  or  joints  are 
produced,  known  as  myotomes  or  mesoblastic  somites. 
From  these  develop  bone,  voluntary  muscle,  and  the 
dermis  of  the  skin. 

While  these  progressive  changes  are  going  on  in  the 
mesoderm,  a  longitudinal  dorsal  groove  develops  in 
the  ectoderm.  By  a  median  fusion  of  the  margins  of 
the  groove,  it  is  transformed  into  a  longitudinal  canal, 
the  neural  canal,  which  develops  into  the  brain  and 
spinal  cord. 

This  brief  embryonic  growth  has  been  productive 
in  specialization  and  differentiation  of  cells.  In  no 
case  will  the  cells  of  one  germ  layer  reproduce,  re- 
place, or  function  for  the  cells  of  any  of  the  other 
layers.  As  derivatives  of  these  three  germ  layers  we 
are  able  to  give  the  following  table  (Minot,  "  Em- 
bryology, "  1903)- 


A  .    ECTODERM. 

B.    MESODERM. 

C.    ENTODERM. 

I. 

Epidermis. 

i.  Mesothelium. 

i.  Notochord. 

(a)  epidermal  appen- 

(a) epithelium  of  per- 

dages. 

itoneum,  pericar- 

(b) lens  of  eye. 

dium,  pleura,  uro- 

genital  organs. 

(b}  striated  muscles. 

2. 

Epithelium  of 

2.  Mesenchyma. 

2.  Epithelium  of 

(a)  cornea. 

(a)  connective  tissue, 

(a)  digestive     tract, 

(b)  olfactory     cham- 

smooth     muscle, 

esophagus,  stom 

ber. 

pseudo  -  endothe- 

ach,    liver,    pan 

(c)  auditory  organ. 
(d)  mouth 
(oral  glands), 

lium,        fat-cells, 
pigment  cells. 
(b)  blood. 

creas,  small  intes 
tine,      yolk-sack 
large       intestine 

(enamel  organ), 

(c)  blood-vessels. 

cecum,      vermix 

(hypophysis^. 
(<?)  anus. 

(d)  lymphatics. 
(e)  spleen 

rectum,   allantois 
(bladder). 

(f)  chorion 

(f)  supporting     tis- 

(b) pharynx,    Eusta 

(fetal  placenta). 

sues,      cartilage, 

chian    tube,    ton 

(g]  amnion. 

bone. 

sils,thymus,para 

(g)  marrow. 

thyroids,  thyroid 

(c)  respiratory  'tract 

3- 

Nervous  system. 

larynx,     trachea 

(a)  brain 

lungs. 

(optic  nerve), 

(retina). 

(b}  spinal  cord. 

(c)  ganglia. 

(d}  neuraxons. 

3 

34       NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 


Vacuoles. 


Spongio  plasm. 
Hyaloplasm. 

Nncleolus. 
Chroma  lift  net-knot. 


Chromatin  network. 

Lin  in  network. 
Nuclear  fluid. 

Nuclear  membrane. 
Cell-membra  ne. 


Exo  plasm. 


Foreign  indosures.     Metaplasm. 
Fig.  12. — Diagram  of  a  cell  (Bohm,  Davidoff  and  Huber). 

THE  CELL. 

More  than  two  hundred  years  ago  the  English 
botanist,  Robert  Hook,  described  cork  as  made  up 
of  "little  boxes  or  cells  distinct  from  one  another." 
In  1838  Schleiden  postulated  a  cellular  basis  for 
plants,  and  according  to  his  conception  these  cells 
were  minute  compartments  filled  with  a  fluid  sub- 
stance in  each  of  which  floated  a  nucleus.  The  fol- 
lowing year,  1839,  Schwann  showed  that  the  animal 
body  was  likewise  built  up  of  cells  resembling  those 
described  by  Schleiden  in  plants.  These  observa- 
tions placed  animals  and  plants  on  a  common  struc- 
tural basis  and  established  the  cell  theory,  now  re- 
garded as  one  of  the  great  biological  discoveries  of 


DEVELOPMENT.  35 

the  eighteenth  century.  Von  Mohl  in  1846  recog- 
nized in  these  cells  a  viscid,  semifluid,  granular  sub- 
stance which  he  named  protoplasm.  Meanwhile 
extensive  observations  by  other  scientists  demon- 
strated the  existence  of  cells  without  cell  walls,  all 
of  which  prepared  the  way  for  Max  Schultze,  who  in 
1 86 1  showed  conclusively  the  identity  of  protoplasm 
in  all  life,  establishing  the  protoplasm  theory,  another 
great  biological  discovery  of  the  eighteenth  century. 
The  conception  of  a  cell,  as  postulated  by  Schleiden 
and  Schwann,  thus  became  modified,  so  that  today 
this  biological  term  stands  for  a  nucleated  mass  of 
protoplasm  which  under  certain  conditions  is  capable 
of  assimilation,  growth,  and  reproduction.  In  some 
cells,  as  certain  bacteria,  no  nucleus  has  been  found; 
however,  in  animal  tissues  as  a  rule,  the  nucleus  is  con- 
stantly present  and  forms  an  essential  part  of  the  cell. 
Whenever  the  nucleus  is  lost  or  destroyed,  the  cell  dies. 
Protoplasm. — Wherever  we  find  protoplasm  we  find 
life,  and  wherever  we  find  life  we  find  protoplasm. 
Protoplasm  is  not  life,  but  all  agree  it  is  the  physical 
basis  of  life.  Every  particle  of  protoplasm  has  its 
origin  in  some  antecedent  protoplasm,  and  so  on,  in 
an  unbroken  series,  all  life  is  traced  back  to  the  earli- 
est primitive  form  of  protoplasm.  This  protoplasm 
is  a  viscid,  transparent,  jelly-like  substance.  It  is  not 
a  substance  of  uniform  physical  and  chemical  proper- 
ties, but  a  mixture  of  many  organic  compounds  which 
in  many  ways  resemble  the  proteid  bodies  or  the  albu- 
mins. It  is  insoluble  in  water,  but  absorbs  water  in 
variable  quantities.  The  protoplasm  of  dry  seeds  may 
contain  but  three  or  four  per  cent,  of  water,  while 


36       NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

in  parenchymatous  or  young  growing  tissues  we  may 
find  ninety-five  per  cent,  of  water.  The  phenomenon 
of  motion  is  common  to  all  protoplasm.  In  plant 
protoplasm  a  streaming  process  is  manifest,  which 
shows  considerable  regularity  as  to  the  direction  of 
the  current  within  the  cell.  This  motion,  as  well  as 
physiological  activities,  is  greatly  modified  by  change 
in  temperature,  and  its  activities  are  also  very  sen- 
sitive to  change  in  intensity  of  light  and  even  to  the 
different  colors  of  light  as  well  as  to  the  actinic  rays. 
It  is  therefore  irritable  in  the  highest  degree. 

Cytoplasm  is  the  name  given  to  the  protoplasm  of 
the  cell  body  or  that  which  surrounds  the  nucleus. 
The  cytoplasm  exhibits  (i)  a  fine  reticulum  of  anas- 
tomosing or  interlacing  threads  or  plates  of  vary- 
ing complexity  called  spongioplasm  or  fibrillar  mass. 
These  threads  are  probably  composed  of  small  par- 
ticles or  granules,  named  microsomes,  that  are  in  close 
touch  with  each  other  and  arranged  in  rows.  The 
other  constituent  of  cytoplasm  is  (2)  a  fluid  sub- 
stance lying  between  the  meshes  of  the  spongio- 
plastic  reticulum,  and  has  been  called  hyaloplasm, 
paraplasm,  or  cytolymph.  Recent  observations  in- 
dicate that  the  microsomes  are  primarily  derived 
from  the  nucleus  and  constitute  the  more  important 
vital  parts  of  the  cell. 

In  some  cells  the  microsomes  are  so  placed  as  to 
give  a  foam-like  structure  to  the  cytoplasm  rather 
than  a  reticular  appearance.  Again,  the  cytoplasm 
of  certain  cells  has  a  homogeneous  watery  appearance 
devoid  of  any  definite  structure.  There  are  therefore 
three  theories  as  to  the  structure  of  protoplasm : 


DEVELOPMENT.  37 

1.  That  it  is  a  fluid  homogeneous  substance. 

2.  That  it  consists  of  minute  spherical  globules, 
like  an  emulsion. 

3.  That  it  is  a  mass  of  interlacing  fibrils,  forming  a 
complex  reticulum. 

In  many  cells  the  protoplasm,  at  or  near  the  sur- 
face, is  quite  dense,  forming  what  is  then  called  the 
ectosarc.  The  more  vicsid  central  portion  is  the 
endosarc. 

In  the  cytoplasm,  usually  by  the  side  of  the  nucleus, 
a  small  body  may  be  found  in  most  cells,  called  the 
centrosome.  The  centrosome  is  occasionally  in  the 
nucleus  and  but  little  larger  than  a  microsome,  being 
usually  surrounded  by  a  clear,  radially  striated  area 
of  protoplasm  called  the  attraction  sphere.  The  cen- 
trosome takes  an  active  part  in  the  multiplication  of 
cells,  but  otherwise  its  function  is  problematic. 

The  cell  wall  is  to  be  regarded  as  a  cell  product. 
In  plant  tissues  the  cell  wall  is  relatively  thick  and 
composed  largely  of  cellulose.  In  animal  tissues  the 
cell  wall  is  unusually  thin,  often  difficult  to  demon- 
strate, and  in  many  cases  absent.  Examples  of  the 
latter  are  amoebas,  white  blood  corpuscles,  nerve  cells, 
and  probably  liver  cells. 

Nucleus. — The  nucleus  is  the  second  constituent 
of  the  cell  and  is  a  round  or  an  oval  protoplasmic 
body  found  floating  in  the  cytoplasm.  Its  shape 
usually  corresponds  to  the  form  of  the  cell,  but  oc- 
casionally C-shaped,  ring-shaped,  and  even  branched 
nuclei  are  found.  Its  position  may  be  eccentric  or 
at  one  end  of  the  cell.  It  has  more  consistency  than 
the  cytoplasm,  but  is  plastic  and  displays  consider- 


38        NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

able  elasticity.  Independent  movement  of  the  nu- 
cleus in  the  cytoplasm  has  often  been  observed.  At 
the  same  time  its  relation  to  the  cytoplasm  is  a  most 
intimate  one  and  many  cytoplasmic  particles  doubt- 
less have  their  origin  in  the  nucleus. 

The  structure  of  the  nuclear  protoplasm  is  even 
more  complex  than  that  of  the  cytoplasm.  A  reticu- 
lum  of  coarse,  thread-like  texture  is  constantly 
present.  This  stains  deeply  and  is  therefore  called 
chromatin.  The  chromatin  threads,  like  the  spongio- 
plasm  of  the  cytoplasm,  are  made  up  of  minute 
particles  or  granules  compactly  arranged  in  rows 
that  cross  and  interlace,  making  nodal  points  here 
and  there  called  nuclear  net-knots.  The  chromatin 
is  imbedded  in  or  deposited  on  a  less  stainable  reticu- 
lum  called  linin,  and  surrounding  both  chromatin 
and  linih  everywhere,  and  filling  their  meshes,  is  a 
semifluid  substance  that  does  not  readily  stain  and  is 
therefore  called  achromatin,  nuclear  sap,  paralininy 
or  karyolymph. 

Imbedded  in  the  achromatic  substance  are  one 
or  more  spherical  bodies  called  nucleoli.  The  nucleoli 
stain  less  heavily  than  the  chromatin  and  may  be 
dissolved  by  reagents  that  do  not  affect  the  chro- 
matin; therefore,  they  are  composed  of  a  substance 
not  identical  with  the  latter.  Their  function  is  not 
known.  The  nucleus  is  usually  enclosed  in  a  thin 
nuclear  membrane  (amphipyrenin)  not  unlike  chro- 
matin material.  This  membrane  has  perforations 
which  allow  a  free  communication  between  the  achro- 
matic fluid  of  the  nucleus  and  the  cytolymph  and 


DEVELOPMENT.  39 

establish  a  most  intimate  relation  between  nucleus 
and  cytoplasm. 

Cell  Inclusions. — Bodies  of  a  solid  nature,  not  pro- 
toplasmic, are  common  to  many  cells.  These  are 
pigments,  oil,  fat,  crystals,  glycogen,  starch,  chloro- 
phyl,  etc.,  and  are  spoken  of  as  cell  inclusions.  The 
last  two  are  found  almost  exclusively  in  plant  cells. 
By  these  inclusions  the  shape  of  the  cell  is  often 
changed,  and  particularly  the  position  of  the  nucleus. 
Fat  gathers  at  one  end  of  the  cell,  crowding  the  nu- 
cleus to  the  opposite  extremity  and  displacing  the 
cytoplasm  to  the  periphery,  mostly  to  that  end  of 
the  cell  occupied  by  the  nucleus.  Pigment  may 
be  in  solution,  more  frequently  in  granules,  and 
always  in  the  cytoplasm,  not  in  the  nucleus.  Vacu- 
oles  are  very  common  to  most  cells.  These  vary  in 
number  and  size  and  are  usually  spherical  cavities 
filled  with  fluid  secreted  by  the  protoplasm.  The 
vacuoles  contract,  often  with  considerable  regularity, 
and,  as  a  rule,  empty  to  the  surface  of  the  cell.  Waste 
products  are  in  this  way  eliminated  from  the  body 
of  the  cell. 

The  constituents  of  a  typical  cell  may  then  be 
summarized  as  follows : 

1.  Cytoplasm,  the  protoplasm  that  surrounds  the 
nucleus,  consisting  of, — 

(a)  Spongioplasm,  a  reticulum  or  fibrillar  network; 
(6)  Hyaloplasm,  a  fluid  portion,  also  called  cy- 
tolymph ; 

(c)  Cell  membrane,  often  absent  in  animal  cells. 

2.  Nucleoplasm  or  karyoplasm,  the  protoplasm  of 
the  nucleus, — 


40       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

(a)  Nuclear  membrane,  frequently  absent; 
(6)  Chromatin,  network  that  stains  easily; 


Diaster. 


Diaster. 


Monastcr.   — 


Resting  nucleus. 
Mctakincsis. 


L —  Diaster. 


Daughter  cells. 


Spirem. 

Fig.  13. — Mitotic  division  of  cells  in  testis  of  salamander  (Benda  and 
Guenther). 

(c)  Linin,  closely  applied  to  the  chromatin,  does 
not  stain ;  dissolves  in  distilled  water ; 

(d)  Nuclear  sap,  a  fluid  perhaps  analogous  to  the 
hyaloplasm ; 

(e)  Nucleolus,  spherical  body  that  stains  heavily; 
(/)    Nuclear  net  knots,  or  karyosomes,  false  nuclei 

that  are  nodal  points  formed  by  interlacing  chro- 
matin network; 

(g)   Nuclear  membrane,  amphipyrennin ; 

(h)  Centrosome,  a  small  spherical  body  often  found 
in  the  cytoplasm  near  the  nucleus.  It  is  looked  upon 
as  the  dynamic  center  in  cell  division. 

Mitosis  or  Karyokinesis. — Mitosis  is  indirect  cell 


DEVELOPMENT. 


41 


division,  and  refers  to  the  changes  manifest  in  the 
nucleus  during  such  division.  The  process  may  be 
divided  into  four  phases — 

i.  Prophase.  The  first  manifestation  of  mitosis 
appears  in  the  centrosome.  This  little  body  is, 
therefore,  looked  upon  as  the  dynamic  center  of  the 
cell.  The  centrosome  divides  and  each  half  passes 
to  opposite  poles  of  the  nucleus.  The  chromatin 
network,  which  really  consists  of  chromatin  granules, 
is  transformed  into  a  skein  of  threads  known  as  a 
spirem  or  mother  skein.  These  threads  break  up  into 
a  definite  number  of  segments  known  as  chromo- 
somes. The  chromosomes  are  even  in  number,  and, 
for  a  given  species,  a  constant  number  is  always 
present.  In  the  human  cell  there  are  sixteen  chro- 
mosomes,— according  to  some,  twenty-four.  To- 
ward the  close  of  this  stage,  each  chromosome 
forms  a  loop  and  is  finally  arranged  symmetrically 
around  the  equator  of  the  nucleus,  with  the  free  ends 
of  each  loop  turned  away  from  the  center.  This 
symmetrical  figure  is  known  as  monaster.  During 
this  stage  the  nuclear  membrane  usually  disappears. 
The  nucleolus  also  vanishes,  just  how  is  not  clear. 
The  net  knots  disappear  with  the  formation  of 
chromatin  loops. 

During  these  changes  the  achromatic  substance— 
linin  and  nuclear  sap — has  formed  a  central  spindle 
with  each  apex  directed  toward  a  centrosome.  This 
spindle  consists  of  fine  threads  or  lines  directed 
toward  the  centrosomes.  A  like  radiation  becomes 
manifest  in  the  cytoplasm,  each  line  being  directed 
toward,  or  from,  one  or  the  other  centrosome.  This 


42       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

radiation  is  absent  from  the  protoplasm  immediately 
surrounding  each  centrosome,  forming  a  clear  field 
called  the  attraction  sphere.  The  lines  that  extend 


Cefllrosome 

tyindle 

wsomt 


e. 


Fig.  14. —  Diagram  of  mitosis. 


into  the  cytoplasm  are  known  as  polar  rays.  Those 
that  form  the  spindle  seem  to  be  attached  to  the 
curved  portions  of  the  chromatin  loops. 

2.  Metaphase. — This  stage  begins  with  the  chro- 
matin loops  arranged  radially  in  the  equatorial  plane 
of  the  nucleus.  The  most  important  change  in 
mitosis  now  takes  place,  in  that  each  chromosome 
loop  divides  lengthwise  to  form  two  daughter  chromo- 
somes. This  is  an  equal  division,  both  qualitative 
and  quantitative.  The  curved  portion  of  each 
daughter  loop  passes  along  the  rays  of  the  achro- 
matic spindle  and  approaches  one  or  the  other  cen- 


DEVELOPMENT.  43 

trosome.     There  are  three  theories  as  to  the  mech- 
anism involved : 

(1)  It  is  affirmed  that  the  threads  of  the  spindle 
contract  and  pull  each  daughter  loop   toward  its 
centrosome. 

(2)  The  rays  or  threads  may  elongate  and  push 
each  loop  toward  the  opposite  centrosome.     Accord- 
ing to  this  theory  there  should  be  twice  as  many  lines 
or  rays  between  the  loops  as  there  are  spindle  rays 
from  each  centrosome,  an  observation  recorded  by 
some  investigators. 

(3)  The  centrosomes  may  be  fermenting  centers 
of  chemical  change,  and  the  explanation,  therefore, 
a  chemical  attraction  or  affinity. 

At  the  close  of  the  metaphase  the  daughter  loops 
arrange  themselves  respectively  around  each  cen- 
trosome forming  what  is  known  as  a  diaster  or 
daughter  star.  The  free  ends  of  these  are  turned 
away,  and  the  curved  portions  of  each  are  turned 
toward  the  centrosome. 

3.  Anaphase. — During   this   period   the   changes 
manifest  in  the  prophase  are  reversed.     The  chro- 
matin  loops  are  gradually  transformed  into  twisted 
skeins    of    threads,    called    daughter   skeins,  which 
ultimately  produce  the  normal  chromatin  reticulum. 
The  nuclear  membrane  and  nucleolus  reappear.     A 
constriction  of  the  cytoplasm  is  manifest  for  the  first 
time.     This  constriction  appears  in  the  plain  passing 
between  the  daughter  nuclei. 

4.  Telophase. — In  this  stage  the  cell  divides  com- 
pletely.    Each  daughter  cell  gradually  assumes  the 
normal  condition  of  the  parent  cell  from  which  it  had 


44       NORMAL   HISTOLOGY  AND    ORGANOGRAPHY. 

its  origin.  The  time  required  for  complete  division 
varies  from  one  to  several  hours. 

Amitosis  is  the  direct  cell  division  and  occurs  sel- 
dom as  a  normal  process.  The  nucleus  merely  con- 
stricts, without  the  formation  of  chromatin  loops  or 
filaments,  thus  producing  two  or  more  nuclei  or 
nuclear  fragments.  The  cytoplasm  may  not  take 
part  in  this  division,  in  which  case  polynucleated 
cells  are  formed;  however,  polynucleated  cells  may 
also  arise  from  mitosis.  Preceding  the  division  the 
nucleolus,  if  present,  may  subdivide,  while  the 
centrosome  does  not  seem  to  take  any  active  part 
whatever.  In  the  human  body  certain  leucocytes 
have  been  described  as  dividing  by  amitosis,  also 
polynucleated  pavement  cells  of  the  bladder.  De- 
generated cancer  cells  have  been  described  as  show- 
ing amitotic  division,  but  whether  a  cause  or  a  con- 
sequence of  degeneration  and  disease  can  be  argued 
with  equal  force.  On  the  other  hand,  certain  em- 
bryonic cells  have  been  described  as  dividing  by 
amitosis,  which  later  take  up  the  regular  cell  di- 
vision of  amitosis,  but  these  cases,  if  normal;  must 
be  regarded  as  very  exceptional. 

Laws  of  Cell  Cleavage.— (i)  The  cleavage  plane  is 
always  equatorial  to  the  nucleus. 

(2)  The  position  of  the  nucleus  depends  on  (a)  the 
shape  of  the  cell,  and  (6)  on  the  distribution  of  food 
material  or  secretions.     If  the  cytoplasm  is  eccentric 
in  the  cell,  the  nucleus  is  associated  with  it. 

(3)  When  each  plane  of  division  is  parallel  to  the 
preceding  plane,  a  filament  is  produced.     This  is  the 
law  in  some  plants,  as  spirogyra,  nostoc,  etc. 


DEVELOPMENT.  4.5 

(4)  When  each  plane  is  at  right  angle  to  the  pre- 
ceding plane  and  in  two  dimensions,  a  surface  of  cells 
is  formed,  as  simple  epithelium. 

(5)  When  each  plane  is  at  right  angle  to  the  pre- 
ceding plane  and  in  three  dimensions,  a  volume  or 
an  organ  is  formed  with  three  dimensions,  as  the 
morula  stage  in  embryos. 

General  Considerations. — The  subject  of  cell  divi- 
sion has  given  rise  to  much  discussion.  While  we 
are  unable  to  control  mitosis,  the  following  are 
factors  that  modify  cell  growth : 

1.  Trauma. — Following  a  cut  or  a  bruise  the  ad- 
jacent cells  are  stimulated  to  rapid  multiplication 
and  the  wound  heals. 

2.  Heat. — There  is  a  mean  temperature  for  the 
maximum  multiplication  of  cells  which  varies  with 
the  species.     In  man  this  mean  temperature  is  blood 
heat,  98.6°. 

3.  Electricity. — By  stimulating  protoplasmic  ac- 
tivity, electricity  no  doubt  is  a  factor  in  influencing 
normal  cell  growth.     Just  how  this  is  accomplished, 
and  to  what  extent,  is  a  much-disputed  problem. 

4.  Light. — A  very  important  factor  in  promoting 
multiplication,  or  decreasing  it,  or  even  destroying 
certain  cells,   as  bacteria.      The   different  rays  of 
light  have  each  a  specific  effect. 

5.  Nourishment. — Proper  food  is  a  stimulant. 

6.  Chemical. — Certain  salt  solutions,    as  sodium 
and  potassium  salts,  have  a  stimulating  effect. 

7.  Exercise. — Regular  systematic  exercise  prompts 
a  healthy  growth.     Massage  acts  in  the  same  way. 
A  laborer,  after  a  day  of  toil,  is  exhausted  because 


46       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

his  cells  are  depleted  and  some  of  them  actually  lost. 
During  his  period  of  rest  new  cells  are  built  up  from 
the  ingested  foods  and  thereby,  practically,  new  tis- 
sues are  formed,  giving  the  feeling  of  comfort  and 
increased  vigor.  The  acquisition  of  new  tissues  is 
an  asset  and  should  be  encouraged. 

Pathological  tumors  are  abnormal  growths  of  nor- 
mal tissues.  In  many  of  these  tumors  the  cells 
multiply  rapidly  by  mitosis,  resulting  often  in  un- 
equal division  of  the  chromosomes,  or  chroma  tin 
loops,  but  whether  this  is  a  cause  or  a  consequence 
can  be  argued  with  equal  force.  We  are  unable  to 
produce  these  tumors  experimentally,  and,  unfor- 
tunately, we  are  often  unable  to  stop  their  mul- 
tiplication of  cells. 

The  surface  of  a  sphere  increases  as  the  square  of 
its  diameter,  while  the  volume  increases  as  the  cube 
of  the  diameter.  As  the  cells  depend  upon  their 
surface  area  for  the  absorption  of  food  and  elimination 
of  waste,  and  as  the  volume  increases  at  a  greater 
rate  than  the  surface  area,  the  reduction  in  size  of  a 
cell  becomes  a  necessity. 

Much  significance  is  attached  to  the  fact  that 
mitosis  brings  about  an  equal  division  of  the  chro- 
matin  or  chromosomes.  If  for  any  reason  an  un- 
equal division  obtains,  the  cell  becomes  abnormal 
and  a  monstrosity,  with  death,  follows.  Experi- 
mentally this  may  be  done  with  an  egg  cell,  which,  if 
anesthetized,  allows  more  than  one  spermatozoon  to 
enter,  resulting  in  an  unequal  division  of  the  female 
pronucleus  and  an  abnormal  development.  That 
chromatin  is  the  bearer  of  hereditary  qualities  is  a 
postulate  based  upon  the  observation  that  mitosis 


DEVELOPMENT.  47 

results  in  an  equal  division  of  the  chromosomes. 
What  these  unrevealed  biological  units  are  is  a 
matter  of  much  controversy. 

Much  work  has  been  done  in  recent  years  on  the 
individuality  of  the  chromosomes,  establishing  the 
fact  that  they  vary  greatly  in  size,  form,  and  con- 
stituents in  one  and  the  same  cell.  Some  are  long 
and  some  are  short,  thick  and  slender,  greatly 
curved  and  nearly  straight,  stain  dark  or  take  only 
a  slight  stain;  in  short,  we  must  now  admit  their 
personnel  and  postulate  special  cell  function  for 
each  chromosome.  Moreover,  it  is  now  practically 
established  that  certain  spermatozoa,  particularly 
in  insects,  have  an  odd  chromosome,  and  that  from 
eggs  fertilized  by  this  particular  class  males  de- 
velop, whereas  from  fertilization  by  spermatozoa 
having  an  even  number  of  chromosomes  females  are 
produced.  In  a  species  of  insect,  Lygceus  bicrucis, 
the  males  develop  spermatozoa  that  have  all  the 
same  number  of  chromosomes,  but  in  one  set  there 
is  present  one  large  chromosome  and  in  the  other 
set  there  is  present  one  small  chromosome.  If  a 
spermatozoon  with  the  small  chromosome  fertilizes 
the  egg,  a  male  develops,  and  if  one  with  the  large 
chromosome  fertilizes  it,  then  a  female  is  formed. 
Sex  chromosomes  have  now  been  recognized  in  a 
large  number  of  males  of  different  groups  of  ani- 
mals, and  we  can,  therefore,  safely  affirm  that  the 
determination  of  sex  rests,  in  most  cases,  with  the 
intrinsic  quality  of  the  fertilizing  spermatozoon. 
Morgan,  therefore,  concludes  that  "  if  these  observa- 


48        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

tions  are  confirmed  they  show  that  in  man,  as  in  so 
many  animals,  an  internal  mechanism  exists  by 
which  sex  is  determined.  It  is  futile  then  to  search 
for  environmental  changes  that  might  determine 
sex."  ("Heredity  and  Sex,"  page  248,  Columbia 
University  Press,  1913.) 


CHAPTER   II. 
TISSUES. 

A  tissue  is  a  complex  of  similarly  differentiated 
cells  and  their  derivatives.  In  all  embryonic  tissues 
and  some  adult  tissues  the  cell  elements  predominate, 
but  in  cartilage  and  bone  and  many  connective  tis- 
sues the  cell  products  make  up  the  bulk  of  the  tissue. 
There  are  four  kinds  of  elementary  tissues, — (i) 
epithelial  tissue;  (2)  Supporting  tissue;  (3)  Muscular 
tissue;  (4)  Nerve  tissue. 

I.    EPITHELIAL  TISSUE. 

Epithelium  lines  surfaces,  external  and  internal, 
and  forms  the  secreting  cells  of  glands.  (See  table, 
Page  33.)  The  cells  of  this  tissue  are  derived  from 
any  one  of  the  three  germ  layers.  Blood  and  lymph 
vessels  do  not  penetrate  between  the  epithelial  cells, 
but  nerve  fibers  enter  the  deeper  strata  and  end  in 
minute  varicosities  that  lie  in  contact  with  many  of 
the  cells.  The  cells  have  a  regular  form,  a  thin  cell 
wall,  and  a  distinct  nucleus  that  is  rich  in  chromatin 
and  therefore  stains  easily  with  hematoxylin.  They 
usually  secrete  a  cement  found  between  adjacent  cells 
which  serves  the  purpose  of  holding  each  cell  firmly  in 
place.  The  cell  wall  is  usually  smooth,  but  in  certain 
places  the  lateral  walls  develop  many  short,  minute 
processes  (prickles)  that  meet  like  processes  from 
adjacent  cells,  forming  intercellular  bridges,  and  be- 
tween the  latter  are  found  intercellular  spaces  filled 
with  nourishing  fluid  for  the  individual  cells.  The 

4  49 


SO       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

cell  rests  upon  a  basement  membrane  that  is  usually 
considered  to  be  made  up  of  basal  processes  of  the 
basal  cells. 

The  free  surfaces  of  epithelial  cells  may  develop 
cilia,  which  serve  the  purpose  of  sweeping  away 
fluids  or  foreign  bodies.  In  many  instances  a  deli- 
cate lining  called  the  cuticle  covers  the  free  ends. 
The  cuticle  is  to  be  regarded  as  a  cell  product,  and 
since  in  many  cases  a  fine  transverse  striation  can 
be  seen,  it  seems  probable  that  the  cuticle  is  built 
from  a  large  number  of  transverse  rods  cemented 


Fig.  15.— Epithelial  cells  from  skin  of  frog.   Surface  view  of  external  layer. 

together.  In  columnar  cells  the  nucleus  is  usually 
found  at  the  basal  end,  thus  being  placed  nearer  the 
blood  and  lymph  supply,  the  nourishing  cell  media. 

Epithelial  tissue  is  classified  as:  (i)  simple  or 
(2)  stratified. 

i.  Simple  epithelium,  consisting  of  a  single  layer 
of  ceils. 

(a)  Simple  squamous,  flat  single  layer  of  cells, 
found  in  the  alveoli  of  the  lung  and  in  Bowman's 
capsule  of  the  kidney. 


TISSUES.  51 

(6)  Simple  cuboidal,  found  forming  the  wall  of 
small  ducts,  portions  of  the  kidney  tubules,  and  the 
vesicles  of  the  thyroid  gland. 

(c)  Simple    columnar,    ciliated    or    non-ciliated. 


Fig.   1 6. —  Squamous  epithelial  cells  from  the  mouth. 

This  is  the  most  common  form  of  simple  epithelium. 
The  alimentary  canal,  below  the  diaphragm,  has 
simple  columnar;  also  portions  of  the  kidney  tubules. 


Murcits. 


Goblet  cell. 

Fig.  17. —  Simple  columnar  cells  from  intestine. 

Simple  ciliated  is  found  in  the  oviduct,  uterus,  cen- 
tral canal  of  the  spinal  cord,  and  smaller  bronchi. 

(d)  Pseudo-stratified.—ln  this  type  all  the  cells 
rest  on  a  common  basement  membrane,  but  the 
nuclei  rest  at  different  levels,  which  give  the  tissue 
the  appearance  of  being  stratified.  Frequently 
this  tissue  is  ciliated,  as  is  the  case  in  portions  of  the 
respiratory  tract. 


52  NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

2.  Stratified    epithelium,    consisting    of    several 
layers  of  epithelial  cells. 


Fig.  1 8. —  Ciliated  epithelium  from  trachea. 


(a)  Transitional,  consisting  of  two  or  three  layers 
of  cells,  found  in  the  wall  of  the  bladder,  ureters, 
pelvis  of  kidney,  and  prostate  portion  of  male 
urethra.  In  this  case  the  surface  layers  of  cells  are 


Pavement  cell. 


Pear-shaped 
cell. 


Pavement  cells. 


Interstitial  cells. 


Fig.   19. —  Epithelial  cells  from  the  bladder. 

flat,  often  poly  nucleated  and  form  a  mosaic  pattern 
upon  the  second  layer,  which  is  pear-shaped,  with 
the  broad  ends  forming  depressions  into  the  first 
layer  of  cells.  The  third  layer  consists  of  smaller, 
irregular,  interstitial  cells  that  fill  the  spaces  between 
the  pointed  ends  of  the  second  row. 


TISSUES. 


53 


(6)  Stratified  Squamous. — In  this  case  the  super- 
ficial layers  are  flat  and  the  deeper  ones  cuboidal 


Pavement  cell. 
Pear-shaped  cell. 

Interstitial  cell. 


Fig.  20. —  Section  of  bladder  epithelium. 

or  columnar.  This  is  the  most  extensive  of  the 
epithelial  tissues.  It  forms  the  epidermis  of  the 
skin,  the  walls  of  the  oral  cavity  and  the  esophagus, 
the  epithelium  of  the 
conjunctiva,  external 
auditory  canal,  va- 
gina, and  the  exter- 
nal sheath  of  hair 
follicles. 

The  outer  cells  be- 
come horny  and  scale 


-=.  ^ -Zrfi^Z; Corneum  or 

-",        horny  layer. 


Stratum 
lucidum. 
\        Stratum 
granule  sum. 


'£>j Malpighian 

2Q  °r  gfr™- 

inal  layer. 


away  quite  regularly 
in  thin  lamellae.  The 
deeper  layers  are  ar- 
ranged to  form  papil- 
lae that  interlock  with 
connective  tissue  pa- 
pillae and  thus  not  only  anchor  the  epithelium  to  the 
subjacent  tissue,  but  increase  the  absorbing  surface 
by  approximating  a  larger  number  of  epithelial  cells 
to  the  underlying  blood  and  lymph  capillaries. 


Fig.  2 1 . — Section  of  epidermis  of  skin 
from  palm-surface  of  finger. 


54 


NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 


(c)  Stratified  columnar,  ciliated  or  non-ciliated. 
This  is  found  in  the  olfactory  mucous  membrane,  the 
first  part  of  many  gland  ducts,  palpebral  conjunc- 
tiva, portions  of  the  male  urethra,  vas  deferens,  and 
portions  of  the  larynx. 

General  Considerations. — The  epithelial  cells  are 
simpler  and  more  embryonic  than  the  cells  of  the 
other  tissues.  They  are  continually  multiplying 

throughout  life,  to  re- 
place the  superficial 
layers  that  are  con- 
stantly exfoliating 
from  the  surfaces.  If 
any  of  these  surfaces 
are  injured,  the  cells 
marginal  to  the  injury 
repair  the  loss  by  a 
gradual  growth  cover- 
ing the  denuded  sur- 
face. As  a  consequence 
of  this  mitotic  activity, 


Fig.  22. — Section  of  stratified  epithe- 
lium from  esophagus. 


we  find  these  cells  fre- 
quently in  pathological  growths  as  epithelial  growths 
or  epithelioma.  If  the  tumor  is  malignant  it  is  a 
carcinoma  or  cancer.  It  is  a  remarkable  fact  that,  in 
the  adult,  epithelium  is  able  to  produce  cells  only 
of  its  own  kind, — i.  e.,  squamous  cells  produce 
squamous  epithelioma,  and  columnar  cells  columnar 
epithelioma.  Epithelial  tissue,  however,  is  easily 
modified,  as  is  evidenced  by  calloused  hands,  pro- 
duced by  heavy  labor,  and  the  cornification  of  nails, 
hair,  horns,  and  teeth. 


TISSUES. 


55 


Since  the  blood  supply  never  penetrates  epithelial 
layers,  it  is  evident  that  the  superficial  layers  of  cells 
receive  less  nourishment  and  ultimately  die,  which, 
perhaps,  accounts  for  the  constant  exfoliation.  It  is 
also  evident  that  anything  that  will  increase  the 
blood  supply  will  increase  the  nourishment,  as  fric- 
tion, massage,  and  hot  applications.  The  nour- 
ishment, at  best,  is  not  very  good,  which  explains  the 


Epithelium  of  cornea. 


Substantia  propria  of 
cornea. 


Fig.  23. — Section  showing  corneal  epithelium  of  the  eye  of  pig. 

ease  with  which  skin  grafts  are  made.  Epithelial 
cells  will  live  for  twenty-four  hours  or  more  in 
normal  salt  solutions,  and  will  even  multiply  in 
favorable  culture  media. 

The  nerve  termination  among  the  epithelial  cells 
is  an  important  relation  which,  in  large  part,  controls 
their  metabolism.  A  disturbed  nervous  system  may 
impair  or  even  cause  a  destruction  of  epithelial  cells. 


56  NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

Cilia  are  exclusively  confined  to  epithelial  cells. 
There  are  three  theories  to  account  for  the  motion 
of  cilia: 

1 .  The  contraction  may  be  intrinsic  in  the  wall  of 
the  cilium.     This  theory  is  supported  by  the  fact 
that  the  cilium  or  flagellum  of  a  spermatozoon  will 
show  motility  when  severed  from  the  rest  of  the  cell. 

2.  Contraction  of  the  base  where  the  cilia  are 
attached.     The  cilia  will  continue  to  vibrate  if  a 
fragment  of  the  cell  protoplasm  remains  attached  to 
them. 

3.  The  cilia  are  supposed  to  be  hollow  tubes  with 
walls  of  unequal  elasticity.     By  forcing  the  proto- 
plasm rapidly  into  these   tubes  ciliary  motion  is 
produced.     Pseudopodia  are  produced  in  this  man- 
ner, and  the  morphological  relation  of  pseudopodia 
and  cilia  is  a  close  one. 

The  one  great  physiological  action  of  epithelium 
seems  to  be  to  secrete  fluids.  Consequently  epithe- 
lium is  found  lining  all  cysts  wherever  the  cyst  is 
located, — in  the  ovary,  the  skin,  or  in  connection 
with  the  alimentary  tract.  Conversely,  a  cyst  may 
be  formed  wherever  epithelium  is  found. 

Lastly,  it  is  of  the  greatest  importance  that  stu- 
dents should  be  able  to  recognize  epithelial  cells. 
The  facts  to  be  remembered  are : 

1 .  That  they  line  surfaces. 

2.  That  they  appear  in  compact  layers. 

3.  The  oval  or  round  distinct  nucleus,   usually 
rich  in  chromatin. 

4.  The  regularity  of  the  cells,  i.  e.,  they  are  of 
one  pattern,  either  squamous,  columnar,  ciliated,  or 
cubical. 


TISSUES.  57 

5.  They  stain  deeply  with  nuclear  stains. 

6.  Their  chief  function  is  to  secrete. 

7.  The  absence  of  blood-  and  lymph- vessels. 

8.  The  presence  of  free  nerve  endings.    While  this 
is  of  no  diagnostic  microscopic  value,  it  is  physiolog- 
ically an  important  relation  to  bear  in  mind.     In 
wounds  and  old  sores  the  epithelial  border  is  the 
most  sensitive  part  and  should  be  carefully  manipu- 
lated to  avoid  inducing  pain. 

Glands. — Much  literature  has  been  contributed 
the  last  years  relative  to  the  proper  conception  as 
to  what  constitutes  a  gland.  The  prevailing  opin- 
ion seems  to  be  that  any  structure  which  secretes  or 
puts  out  a  product  that  is  not  used  directly  in  the 
metabolism  of  the  body  should  be  called  a  gland. 
If  the  fluid  is  a  waste,  the  product  is  an  excretion; 
if  it  has  a  utility,  it  is  a  secretion.  Accordingly, 
mucous  and  synovial  and  serous  membranes  are 
glandular  structures  as  well  as  the  liver,  the  pan- 
creas, or  the  kidney.  Furthermore,  the  simplest 
form  of  a  gland  is  a  single  secreting  cell  situated 
apart  by  itself,  and  such  unicellular  glands  are  quite 
common  in  invertebrates  and  are  represented  in  man 
by  the  goblet  cells  found  in  mucous  membranes. 
Epithelial  cells  are  the  chief  secreting  cells  of  the 
body,  and  these  cells,  therefore,  form  the  glandular 
tissue  of  all  glands  except  the  lympho-glandulcz, 
which  is  a  connective- tissue  production.  The 
lymph  glands  thus  constitute  a  class  entirely  by 
themselves  as  distinguished  from  all  other  forms, 
which  may  be  called  epithelial  glands.  As  one  of 
the  important  functions  of  lymph  glands  is  to  con- 
tribute white  blood-corpuscles  and  thus  scatter  its 


58        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

own  cells,  they  may  also  be  called  dehiscent  or  cyto- 
genic  glands,  a  term  applicable  to  the  testes  and 
ovaries,  which  are  epithelial  glands  that  perform  a 
similar  function  by  putting  out  their  own  cells  in 
the  form  of  spermatozoa  and  ovules. 

Numerous  goblet  cells  are  found  in  the  simple 
epithelium  lining  the  stomach  and  intestines,  and 
are  particularly  abundant  in  the  lower  part  of  the 

bowel.  These  cells  func- 
tion as  glands  and  secrete 
mucus  for  the  protection 
of  the  surface.  In  case 
of  irritating  media,  such 
as  undigested  food  or 
poisons,  extensive  mucus 
is  poured  out  over  the 
surface,  thus  protecting 
the  delicate  inner  lining. 
In  some  cases  of  consti- 
pation this  mucous  secretion  is  impaired.  Salts 
or  drugs  that  increase  the  functional  activity  of  these 
cells  correct  such  complication.  On  the  other 
hand,  too  extensive  a  secretion  may  be  corrected  by 
drugs,  as  opiates,  that  inhibit  the  physiological 
action  of  these  cells.  Constipation  may  be  due 
to  inertness  of  the  musculature  of  the  intestinal 
wall,  in  which  case  other  remedies  correcting  this 
disturbance  are  indicated — massage,  hydrotherapy, 
and  drugs  that  act  on  the  musculature. 

Physiologically,  many  gland  cells  are  either  mu- 
cous or  serous.  In  mucous  cells  the  mucus  secretion 
collects  at  one  extremity  of  the  cell  as  a  clear,  glisten- 


Serous  gland.  Mucous  gland. 

Fig.  24. —  Skin  and  simple  alveolar 
glands  from  the  salamander. 


Tissues.  59 

ing  drop.  The  cytoplasm  and  nucleus  are  crowded 
to  the  opposite  end.  In  serous  cells  the  nucleus  is 
more  centrally  placed,  and  the  serous  secretion  is 
stored  up  as  minute  granules  distributed  through- 
out the  cytoplasm,  more  especially  in  that  por- 
tion of  the  cell  lining  the  free  surface.  Some 


Crypt. 


Parietal  cell. 


Chief  cell. 


Fig.  25. —  Simple  tubular  gland  from  stomach. 

glands  are  mucous,  some  are  serous,  and  some  are 
mixed. 

Mucous  Membrane. — A  mucous  membrane  con- 
sists of  a  lining  of  epithelial  cells,  basement  mem- 
brane, and  membrane  propria.  The  basement  mem- 
brane is  largely  an  elastic  cellular  secretion  on  which 


60        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

the  epithelial  cells  rest,  although  at  times  flattened 
connective-tissue  cells  seem  to  enter  into  its  forma- 
tion. The  membrana  propria  is  a  connective-tissue 
production  consisting  of  connective-tissue  cells, 
fibers,  and  blood-  and  lymph- vessels.  Mucous  mem- 


Demilune  of  Heidenhain. 

Fig.  26. —  Cells  from  different  glands  :    a,  Pancreas;    b,  submaxillary 
gland;  c,  liver. 

branes  line  cavities  or  tubes  that  communicate  with 
the  surface  of  the  body,  such  as  the  alimentary  canal, 
respiratory  tract,  and  urogenital  system. 

Serous  Membrane. — A  serous 
membrane  has  the  same  histo- 
logical  elements  as  the  mucous 
membrane.  The  epithelial  lining 
is  simple  squamous,  and  these 
cells  secrete  a  serous  fluid,  more 
viscid  and  more  of  a  lubricant 
than  mucus.  Serous  membranes 
enclose  cavities  that  do  not  com- 
municate with  the  surface  of  the 
body,  as  the  pleural,  pericardial,  and  peritoneal 
cavities  and  cavities  of  joints,  forming  in  the  latter 
case  synovial  membranes.  Sheaths  or  bursae  of 
tendons  have  serous  membranes. 


Cell  empty 
of  secretion. 

Fig.  27. —  Goblet  or 
mucous  cells  from  intes- 
tine. 


TISSUES. 


61 


As  to  form,  epithelial  glands  are  classified  as — 
i.  Simple. 

(a)  Simple  tubular — gastric  glands,  sweat 
glands,  and  uterine  glands. 


alveolar  Stmfile  cdoeolarr 

Fig.  28. —  Diagram  of  different  forms  of  glands. 

(b)   Simple    alveolar — smallest     sebaceous 
glands,  and  skin  glands  in  amphib- 
ians. 
2.  Compound. 

(a)   Compound  tubular — kidney,  liver,  testis. 


62        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

(6)  Compound  alveolar  or  racemose — sali- 
vary glands,  mammary  gland,  lung, 
pancreas,  sebaceous  glands. 

Glands  not  included  in  this  classification  are  uni- 
cellular glands  and  secreting  membranes,  which  can- 
not be  classified  as  to  form.  Lymph  glands,  which 
are  of  connective-tissue  origin,  and  like  the  testis  or 
ovary,  may  be  called  dehiscent  or  cytogenic  glands. 
Follicular  glands,  such  as  the  thyroid  gland,  and  the 
ductless  glands,  producing  internal  secretions,  such 
as  the  hypophysis  cerebri,  thyroid  gland,  suprarenal 
gland,  areas  of  Langerhans  of  the  pancreas,  inter- 
stitial cells  of  the  testis,  and  corpora  lutea  of  the 
ovary.  The  thymus  gland  and  spleen  are  lymphoid 
organs,  and  therefore  to  be  classified  among  the 
lympho  glandules . 

The  object  of  any  anatomical  classification  is  to 
simplify  and  correlate  structural  facts.  From  the 
foregoing  outline  it  is  clear  that  glands,  according  to 
modern  views,  embrace  such  a  complex  of  structures 
that  any  classification,  either  according  to  origin,  or 
form,  or  tissues,  or  even  function,  does  not  accom- 
plish the  end  in  view,  namely,  simplicity.  The  dif- 
ficulty met  with  is  due  to  the  fact  that  our  con- 
ception of  a  gland  rests  largely  with  the  physiolog- 
ical action  of  gland  cells  rather  than  with  any  com- 
mon intrinsic  anatomical  quality. 

Endothelium. — This  term,  introduced  by  His  in 
1865,  is  generally  applied  to  the  layer  of  cells  that 
line  closed  cavities,  such  as  peritoneal  and  pleural 
cavities,  circulatory  system,  and  cavities  of  joints. 


TISSUES. 


These  cells  thus  form  the  inner  layer  of  serous  mem- 
branes, and  while  structurally  they  bear  a  close  re- 
semblance to  epithelial  cells,  there  is  nevertheless  an 
intrinsic  difference  made  apparent  by  a  comparison 
of  pathological  growths  from  these  cells  called  endo- 
thelioma,  and  like  growths  from  epithelial  cells  called 
epithelioma.  Endothelioma  are  usually  slower  of 
growth,  less  malignant  when  malignancy  exists,  and 
have  a  tendency  to  form  mucoid  deposits.  Endothe- 
lial  cells  are  mononucleated, 
scaly,  or  of  the  pavement 
variety  with  wavy  borders, 
and  are  held  together  with  a 
cement  substance  that  re- 
quires special  staining  tech- 
nique to  demonstrate.  They 
impart  a  transparent,  smooth, 
glistening  surface  to  the  mem- 
brane which  they  clothe. 

Peritoneum  and  Pleura.— 
These  are  true  serous  mem- 
branes, the  structure  of  which 
is  described  on  page  60.  Elas- 
tic fibers  are  particularly  abundant  in  the  membrana 
propria,  giving  strength  to  both  peritoneum  and 
pleura,  so  that  these  membranes  are  readily  sewed 
in  surgical  cases.  Physiologically  these  membranes 
are  of  the  greatest  importance : 

i.  It  is  claimed  that  the  simple  pavement  epithe- 
lial cells  of  the  peritoneum  can  produce  a  secre- 
tion that  clots,  and  in  this  manner  adhesions  are 


Fig.  29. — Epithelium  or 
endothelium  from  mesentery. 
Silver  nitrate  stain. 


64        NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

quickly  formed.  This  is  of  the  greatest  importance 
in  preventing  the  spreading  of  an  infection,  as  in 
peritonitis. 

2.  These  cells  act  as  phagocytes  and  feed  upon 
bacteria  in  case  of  an  infection.  According  to  one 
view  they  can  destroy  living  bacteria.  A  second 
theory  is  that  they  act  as  scavengers  and  remove 
only  dead  bacteria. 

Stomata  and  stigmata  have  been  frequently  de- 
scribed as  minute  openings  in  these  membranes  to 
facilitate  the  absorption  of  fluids.  Stomata  are 
said  to  have  guard  cells  to  regulate  the  size  of  the 
opening,  and  were  supposed  to  be  specially  abundant 
in  the  peritoneal  lining  of  the  diaphragm.  The  exist- 
ence of  stomata  has  lately  been  strenuously  denied. 
The  rapid  absorption  of  peritoneal  fluid  is  a  well- 
established  fact.  If  stomata  are  absent  the  ab- 
sorption is  purely  one  of  osmosis  or  dialysis.  It 
should  be  remembered  that  drainage  is  along 
lymphatic  channels  and  therefore  from  the  pelvis 
toward  the  thorax. 

II.    SUPPORTING  TISSUE. 

The  embryonic  connective  tissue  is  largely  cellular, 
but  in  the  adult  body  the  intercellular  substance 
greatly  predominates  and  gives  the  characteristics 
on  which  a  classification  is  based.  The  cell  elements 
are  but  slightly  modified  from  the  embryonic  type, 
but  the  cell  products  or  intercellular  substance  be- 
come modified  to  form  bone,  cartilage,  or  connective- 
tissue  fibers.  The  difference  here  is  relatively  a  dif- 


TISSUES.  65 

ference  in  the  degree  of  condensation  of  the  inter- 
cellular substance,  being  either  loosely  arranged  as 
in  reticular  connective  tissue,  or  more  compact  as  in 
tendons,  or  a  greater  degree  of  condensation  as  in 
cartilage,  bone,  and  dentine.  In  all  these  types  the 
cellular  elements  are  morphologically  very  similar, 
which  makes  it  possible  for  one  form  to  develop  into 
that  of  another;  for  instance,  bone  is  produced  from 
cartilage,  or  from  fibrous  connective  tissues. 

The  function  of  supporting  tissue  is  largely  a  pas- 
sive one  depending  on  its  physical  properties,  and  the 
amount  of  nourishment  the  cellular  elements  re- 
ceive is  therefore  a  very  variable  quantity.  Ten- 
dons, particularly,  have  a  limited  supply,  perhaps 
because  the  cells  form  so  small  a  part  of  these  struc- 
tures. Nutrition  is  supplied  from  the  lymph  which 
penetrates  the  ground  substance  through  clefts  or 
minute  channels  placed  in  the  intercellular  material 
of  the  more  condensed  forms.  In  bone  fine  canals 
develop  and  anastomose  to  form  a  canalicular  sys- 
tem, while  in  other  forms,  as  mucous  connective  tis- 
sue and  hyaline  cartilage,  the  nourishing  lymph 
seems  to  pass  through  the  ground  substance  regard- 
less of  lymph  channels,  as  in  these  cases  the  latter 
have  not  been  found. 

Blood  vessels  and  capillaries  ramify  more  or  less 
freely  through  the  matrix  of  supporting  tissue,  ex- 
cept in  case  of  cartilage,  where  they  are  practically 
absent.  Unlike  epithelia,  nerves  may  be  abundant, 
but  in  no  case  do  nerve  fibers  unite  with  the  cellu- 
lar elements ;  however,  special  sensory  nerve  endings 

5 


66        NORMAL   HISTOLOGY  AND    ORGANOGRAPHV. 

are  frequently  found,  particularly  in  the  connective- 
tissue  elements. 

Fat  in-  the  human  body  is  mostly  found  stored 
up  in  modified  connective-tissue  cells.  This  may 
occur  wherever  there  is  connective  tissue,  and  fat 
cells  must  therefore  be  regarded  as  modified  connec- 
tive-tissue cells.  Likewise  certain  pigment  cells 
and  red  blood  corpuscles  belong  to  this  class. 

The  supporting  tissue  is  derived  exclusively  from 
the  mesenchyma,  a  subdivision  of  the  middle  germ 
layer  or  mesoderm.  It  is  divided  into  three  classes — 

connective  tissue,  carti- 
lage, and  bone. 


Fig.  30. — Connective-tissue  cells  from  Fig.     31. — Connective-tissue 

a  chick  embryo.  cells  from  Wharton's  jelly  of 

the  umbilical  cord. 

1.    CONNECTIVE  TISSUE, 

The  elements  of  this  tissue  consist  of  cells  and  cell 
products,  in  the  form  of  connective-tissue  fibers, 
which  penetrate  and  give  consistency  and  support  to 
every  organ  in  the  body. 

i .  Connective-tissue  Cells. 

(a)  Embryonic  Connective-tissue  Cells. — These  are 
irregular,  stellate  cells  found  in  embryos  and  in  the 
umbilical  cord.  Those  of  the  cord,  with  the  matrix  in 
which  they  are  imbedded,  form  a  soft,  pulpy  mass 


TISSUES.  67 

known  as  Wharton's  jelly,  or  mucous  tissue.  These 
cells  are  loosely  associated  in  no  definite  order,  their 
stellate  processes  interlace  and  sometimes  appeal 
•to  come  in  direct  contact.  Their  nuclei  are  round, 
or  oval,  or  elongated,  forming  what  is  known  as  the 
spindle-shaped  and  pointed  nucleus,  often  resem- 
bling the  cigar-shaped  and  rounded  nucleus  of  a  plain 
muscle  cell.  The  nuclei  are  rich  in  chromatin,  and 
therefore  stain  heavily  with  hematoxylin.  Blood- 
and  lymph- vessels  mingle  freely  with  these  cells;  in 


Fig.  32. — Two  pigment  cells  from  the  dermis  of  a  salamander.     The 
pigment  is  in  the  cytoplasm. 

fact,  this  association  is  constant.  The  so-called 
granulation  tissue  in  healing  wounds  consists  of  em- 
bryonic connective-tissue  cells,  always  bleeds  easily, 
because  of  its  vascularity,  and  painless  because  of 
absence  of  nerve  endings. 

(b)  Pigment  Cells. — These  are  connective-tissue 
cells  in  which  pigment  is  stored  in  the  cytoplasm, 
never  in  the  nucleus.  The  cells  are  extensively 
branched,  large  and  flat.  In  amphibians  and  rep- 
tiles they  are  abundant  in  the  dermis  of  the  skin,  and 
enable  the  animal  to  change  its  color,  as  is  the  case 
with  the  tree  toad  and  the  chameleon.  In  the  human 


68       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


Fig.  33. — Pigment  cells  from 
the  choroid  coat  of  the  eye. 
These  cells  are  of  connective- 
tissue  origin. 


body  connective-tissue  pigment  cells  are  limited  to 
the  choroid  coat  and  iris  of  the  eye,  to  birth-moles, 
and  to  the  piamater  of  the  brain.  The  pigment 
may  be  of  any  color,  the  constituent  being  melanin, 
a  coloring  material  probably  derived  from  the  blood. 

(c)  Fat  Cells. — These  are 
connective-tissue  cells  with 
a  large  storage  of  fat.  The 
fat  occupies  the  center  of 
the  cell  as  a  big  drop  which 
crowds  the  cytoplasm  and 
nucleus  to  one  side,  closely 
pressed  against  the  cell 
wall,  which  is  unusually 
conspicuous.  The  cells 

are  large  and  spherical.  Since  fat  is  dissolved  by 
alcohol,  these  cells  in  sections  are  distorted,  polyhe- 
dral, and  appear  more  like  irregular  spaces  than  any- 
thing else.  Normal  fat  is 
not  to  be  confounded  with 
pathological  fat  found  in 
fatty  degeneration  of 
organs.  In  the  latter  case 
the  fat  appears  as  little 
droplets  diffused  through 
the  cytoplasm  of  the  dis- 
eased cells,  and  is  pro- 
duced at  the  expense  of  protoplasm,  a  destructive 
process  or  katabolism.  Normal  fat  is  a  constructive 
process  or  anabolism,  and  is  therefore  a  storage  of  food 
or  potential  energy.  Its  production,  physiologically, 
is  not  clearly  understood.  It  may  be  produced  from 


Fat. 


Cytoplasm. 


Nucleus. 
Fig.  34. — Normal  fat  cell. 


TISSUES.  69 

a  proteid  diet,  but  its  production  is  more  easily 
prompted  by  a  fatty  diet  and  the  carbohydrates. 
Cold  prompts  its  production,  as  is  clearly  manifest 
in  hibernating  animals  when  the  cold  season  ap- 
proaches, and  the  increased  weight  of  animals,  as  a 
rule,  during  the  winter  season. 

Connective-tissue  cell. 


Nucleus  of  fat  cell. 


Fig-  35- — Fat  cells  as  they  appear  in  sections  treated  with  alcohol. 
Alcohol  dissolves  the  fat. 

The  usual  stain  for  fat  is  osmic  acid,  in  which  fat 
acts  as  a  reducing  agent,  precipitating  black  osmium. 
Any  reducing  agent  will  do  this,  as  is  made  evident 
by  the  black  color  of  the  cork  in  a  bottle  containing 
osmic  acid  solution,  fat  being  absent  from  cork. 

Other  connective-tissue  cells,  as  Plasma  cells,  Wan- 
dering cells,  and  Mast  cells,  are  frequently  described. 
These  resemble  normal  constituents  of  blood  and 
lymph  to  which  they  may  belong. 

2.  Connective-tissue  Products.  —  These  products 
may  be  a  jelly-like  substance  or  fibers.  Connective- 
tissue  cells  are  always  associated  with  these  products. 
There  are  two  theories  as  to  the  production  of  fibers. 

(a)  The  fibers  may  be  processes  of  the  cytoplasm 
that  lose  their  cell  connection. 


70       NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 


(b)  The  connective-tissue  cells  may  secrete  a 
homogeneous  matrix,  which  later  becomes  striated, 
producing  fibers  in  a  manner,  as  fibrin  is  formed  in 
clotting  blood. 

Connective  tissue  is    classified 
according  to  its  matrix  into : 

i.  Mucous  Connective  Tissue. 
—This  consists  largely  of  embry- 
onic connective-tissue  cells  and 
a  jelly-like  matrix  or  ground  sub- 
stance which  gives  a  reaction  for 
mucus.  It  is  found  in  the  um- 
bilical cord,  where  it  is  known  as 
Wharton's  jelly,  and  in  embry- 
onic tissue. 

2.  White  Fibrous  Connective  Tissue. — This  consists 
largely  of  white  nonelastic  fibers.  The  fibers  are 
parallel  to  each  other,  not  branched,  and  yield  gela- 


Fig.  36.  —  Reticular 
tissue  from  a  lymph 
gland. 


Tendon 
cell. 


Fig-  37- — Teased  tendon,  showing       Fig.  38.— Cross  section  of  tendon, 
fine  wavy  white  fibers. 

tin  on  boiling.  The  fibers  swell  up  when  treated  with 
acetic  acid.  They  are  found  in  tendons,  the  apo- 
neuroses,  and  ligaments,  the  fascia  of  muscles,  the 
dura  mater,  and  the  fibrous  capsules  of  many  organs. 


TISSUES. 


3.   Yellow  Fibrous  Connective  Tissue. — The  matrix 
in  this  consists  of  elastic  fibers  that  are  branched, 
and  usually  coarser  than 
the  white  nonelastic  fibers. 
They  do  not  swell  up  when 
treated   with    acetic    acid  ^ 
and  yield  elastin  on  boil- 
ing.    Like  the  preceding, 
the   fibers   are  frequently 
grouped  into  bundles  with 
a  limited  supply  of  blood- 
vessels   and     connective- 
tissue   cells.      This   tissue 

is  found  wherever  elasticity  is  required,  as  in  the 
ligamentum  nuchae   and   subflava,  in   the  walls   of 


Fig.    39. — Longitudinal   section 
of  tendon. 


Fig,  40.— a,  Yellow  elastic  fibers  from  the  teased  ligamentum  nuchae 
of  the  ox;  b,  Cross-section  of  a  portion  of  the  ligamentum  nuchae  of  the 
ox.  The  elastic  fibers  are  grouped  in  bundles  with  a  few  intervening 
connective-tissue  cells. 

arteries,  and  in  the  membrana  propria  of  the  peri- 
toneum and  pleura. 

4.  Reticular  Connective  Tissue. — This  is  a  reticu- 


72  NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

lum  of  interlacing  fibrils  and  is  found  in  adenoid 
tissue,  lymph  nodes,  spleen,  and  membrana  propria 
of  mucous  membranes.  Also,  to  a  limited  extent,  in 
bone  marrow. 

5.  Areolar  Connective  Tissue. — This  is  really  a  mix- 
ture of  interlacing  bundles  of  white  and  yellow 
elastic  fibers.  It  is  found  subcutaneously  to  the 
skin,  to  which  it  imparts  elasticity.  Areolar  tissue 
is  vascular  and  favors,  therefore,  a  rapid  spread  of 
bacteria.  Over  bony  prominences  there  is  a  limited 
supply  of  areolar  tissue  and  the  skin  at  these  places 

has  restricted  mobility.  It 
is  at  these  points  that  the 
spread  of  an  infection,  such 
as  erysipelas,  is  checked. 

General  Considerations. 
—On  account  of  the  embry- 
onic condition  of  connec- 
tive-tissue cells  these,  like 

Fig.  41. — Elastic  fibers  of  the 

mesentery.  epithelial    cells,    are    fre- 

quently met  with  in  patho- 
logical tumors.  If  the  tumor  is  malignant  it  is 
called  a  sarcoma,  and  is  as  fatal  to  life  as  carcinoma, 
or  cancer.  If  the  tumor  is  made  up  largely  of  fat 
cells,  it  is  called  a  lipoma,  and  if  the  fibrous  elements 
predominate  it  is  a  fibroma. 

The  production  of  connective  tissue  is  often 
nature's  method  of  checking  the  spread  of  a  disease. 
This  tissue  is  produced  as  a  wall  in  advance  of  a 
spreading  infection,  and  if  the  bacteria  are  unable  to 
penetrate  this  barrier,  the  disease  soon  becomes  self- 
limiting.  This  accounts  for  the  swollen  infected 


TISSUES.  73 

parts,  and  also  for  the  redness,  which  is  due  to  the 
extensive  blood  supply  which  is  always  associated 
with  this  tissue.  Such  a  swollen  tumor  represents 
an  induration  and  a  congestion.  In  this  manner  a 
whole  or  a  part  of  an  organ  may  be  affected.  The 
connective-tissue  fibers  are  absorbed  with  difficulty 
or  not  at  all,  and  a  permanent  mark  or  scar  remains 
as  an  evidence  of  the  injury.  In  a  healing  wound, 
particularly  if  infected,  these  fibers  are  abundantly 
produced,  and  its  redness  is  evidence  of  its  extensive 
vascularity  or  blood  supply.  Later,  these  fibers  con- 
tract, which  occludes  the  blood,  and  then  the  color 
changes  from  a  red  to  a  white  scar  that  no  medical 
treatment  can  remove. 

Pigmentation  is  a  most  important  subject.  Pig- 
ment appears,  as  a  rule,  in  the  cytoplasm  of  cells, 
seldom  between  the  cells.  It  is  not  confined  to  con- 
nective-tissue cells,  but  is  common  to  epithelial  cells, 
as  the  deep  layer  of  the  epidermis  giving  the  color  of 
races ;  is  found  in  the  retina  cells,  where  it  is  always 
black,  and  in  hair  and  nails.  It  appears  in  the  cyto- 
plasm of  muscle  cells,  particularly  in  old  heart 
muscle,where  it  is  found  near  the  ends  of  the  nuclei, 
and  is  nearly  always  present  in  nerve  cells,  giving  a 
gray  color  to  this  tissue.  Pigmentation  is  an  ac- 
companiment of  many  diseases,  particularly  skin 
diseases.  It  is  also  produced  under  the  influence  of 
light,  as  freckles,  that  can  only  be  removed  by  the 
normal  exfoliation  of  the  epithelium. 

The  production  of  pigment  seems  to  depend  upon 
the  blood.  As  blood  is  absent  from  epithelium  there 
are  two  theories  as  to  the  manner  in  which  the  cells 
obtain  it:  (a)  they  may  receive  it  directly  from  the 


74       NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

blood,  or  (6)  connective-tissue  cells  may  elaborate 
it  and  deliver  it  secondarily  to  the  epithelial  cells. 
That  the  pigment  is  not  intrinsic  to  epithelial  cells  is 
proved  by  the  fact  that  colored  skin  grafted  on  a 
white  man  soon  turns  white,  and  white  skin  grafted 
on  a  colored  person  turns  black.  The  fruitless*  at- 
tempts to  change  one's  color  are  well  known. 

A  melanotic  sarcoma  'is  a  pigmented  connective- 
tissue  tumor,  very  malignant,  whose  cells  disseminate 
very  rapidly  throughout  the  body,  producing  every- 
where new  tumors.  These  cells  have  their  origin 
from  normal  pigmented  connective-tissue  cells,  and 
therefore  are  supposed  to  come  from  birth-marks,  or 
the  choroid  of  the  eye,  or  the  piamater  of  the  brain. 
The  etiology  of  such  tumors  is  unknown.  Fortu- 
nately they  are  rare. 

The  facts  to  be  remembered  in  regard  to  con- 
nective tissues  are:  i.  The  easily  stained  round,  or 
oval,  or  spindle-shaped  nucleus.  2.  The  cells  are 
loosely  thrown  together,  not  in  compact  layers  or 
strata.  3.  The  stellate  cells,  although  the  processes 
are  often  inconspicuous  and  not  readily  detected. 

4.  The  tissue  is  vascular  where  cells  are  abundant. 

5.  The  .absence  of  free  nerve  endings  as  among  epi- 
thelial cells.     6.  They  do  not  secrete  as  do  the  epi- 
thelial cells. 

2.  CARTILAGE. 

Cartilage  is  supporting  tissue  in  which  the  inter- 
cellular substance  predominates  and  yields  chondrin 
upon  boiling.  The  cartilage  cells  are  typical  con- 
nective-tissue cells,  and  occupy  lenticular  spaces  in 
the  matrix  called  lacuna.  Cartilage  is  surrounded 
by  a  dense  connective-tissue  membrane  called  the 


TISSUES. 


75 


perichondrium,  in  which  smaller  blood-vessels  ramify. 
Blood-  and  lymph-vessels  are  absent  from  the  carti- 
lage matrix,  except  rarely  and  in  places  where  active 
growth  or  ossification  is  going  on  they  may  be  present. 
According  to  the  structure  of  the  matrix,  cartilage  is 
classified  as,—  

Perichondrium . 


Lacuna. 

Cartilage  cell. 
Cartilage  matrix. 


Fig.  42. — Section  of  hyaline  cartilage  from  the  trachea. 


i.  Hyaline  Cartilage.— This  is  the  simplest  and 
most  common  form  of  cartilage.     The  matrix  appears 


Matrix. 


Cells. 


Lacuna. 


Fig  4, —TWO  groups  of  cells  from  hyaline  cartilage:  A , .Two 
cells  found  just  beneath  the  perichondrium;  B,  Four  cells  found  deeper 
in  the  cartilage  matrix. 

to  be  a  homogeneous  substance,  although  many  fine 
interlacing  fibrils  are  present.  The  lacunae  near  the 
perichondrium  have  their  long  axis  parallel  to  the 


76       NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 


surface,  while  deeper  in  the  matrix  the  long  axis  is 
often  at  right  angles  to  the  surface.  Each  lacuna 
contains  one  or  more  cartilage  cells.  The  cartilage 

surrounding     lacunae 
usually  stains  differ- 

Cartilase  cell. 


Elastic  fibers. 


ance  of  the  matrix. 

This  cartilage  oc- 
curs as  articular  carti- 
lage of  joints,  at  the 
end  of  ribs,  and  in  the 
nose,  the  larynx,  the 
Fig.  44.—  Section  of  elastic  cartilage  trachea,  and  bronchi. 

from  epiglottis.  2     Elastic     Carti. 

lage.  —  Elastic  cartilage  differs  from  the  hyaline  vari- 

ety in  having  typical  interlacing,  branched  elastic 

fibers  that  form  a  dense  network.    This  cartilage  is 

found  wherever  elas- 

ticity is  required,  as  in 

the  external  ear,  the 

Eustachian  tube,  epi- 

glottis,   part  of   ary- 

tenoid  cartilages,  and 

cartilag'es  of  Wrisberg 

and  Santorini. 

3.  White  Fibrous 
Cartilage.  —  In  this  va- 
riety the  white  fibers 
predominate.  As  a  rule  these  fibers  run  parallel  in 
bundles  and  do  not  branch.  A  granular  matrix 
intervenes  between  the  fibers.  Fibrous  cartilage 
is  found  in  the  intervertebral  disc,  in  the  sym- 


Fig.    45  —  Section  of   white   fibrocarti- 
lage  from  symphysis  pubis. 


TISSUES.  77 

physis  pubis,   and  in  the  insertion  of  the  round 
ligament. 

General  Considerations. — Cartilage  tumors  are 
known  as  chondroma,  and  are  common.  Like 
cartilage  they  are  of  slow  growth  and  therefore 
harmless.  The  absence  of  blood  accounts,  in  large 
part  for  the  inactivity  of  the  cartilage  cells,  both  in 
the  normal  and  pathological  condition.  Further- 
more, cartilage  cells  are  enclosed  in  the  matrix  in  a 
manner  that  inhibit  their  multiplication.  Cartilage 
therefore  grows  by  apposition  or  acquisition,  not  by 
intussusception,  like  most  tissues. 

Cartilage  slowly  ossifies  with  age.     During  this 
process  loops  of  blood-vessels  enter  the  matrix  from 
the  perichondrium,  and  lime  salts  are  deposited  ad- 
jacent to  the  cartilage  cells.     This  process  will  be 
-further  described  under  bone  development. 

The  identification  of  cartilage  is  very  easy,  as  the 
matrix  has  a  marked  affinity  for  many  stains. 
3.  BONE. 

Bone  is  the  chief  supporting  tissue  of  the  body, 
and  consists  of  a  calcified  intercellular  substance, 
mostly  calcium  phosphate,  and  connective-tissue 
cells,  or  bone  cells.  Organic  substance  constitutes 
one-third  the  weight,  and  inorganic  substance  two- 
thirds  the  weight  of  bone.  The  bone  cells,  some- 
times called  bone  corpuscles,  are  flattened  stellate 
cells  with  many  slender  processes,  and  a  well  defined 
round  or  oval  nucleus.  Like  cartilage  cells  they  lie 
imbedded  in  lenticular  spaces  called  lacuna.  These 
lacunae,  however,  communicate  with  adjacent  la- 
cunae by  means  of  numerous  capillary  tubes  called 


78        NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

canaliculi,  into  which  extend  the  slender  cell  proc* 
esses.  Through  these  canaliculi  the  imprisoned 
cells  receive  their  nourishment  and  give  up  their 
waste  products. 

Haversian  System. — This  consists  of  a  Haversian 


Haversian  canal. 


Fig.  46. — Haversian  system  with  only  one  lacuna  sketched. 

canal,  containing  an  artery,  vein,  and  nerve,  bone 
lamallae  concentrically  arranged  around  the  canal,  and 
from  two  to  six  rows  of  concentrically  arranged  cells 
with  their  lacunae  and  canaliculi.    The  canals  average 
0.05  mm.  (5-^  inch)  in  diameter. 
The  canals,  as  a  rule,  run  parallel 
with  the  shaft  of  the  bone,  but  com- 
municate freely  with  each  other. 
The  blood  penetrates  as  far  as  the 
Haversian  canals  but  the   lymph 
reaches  each  bone  cell  through  the 
finer  canaliculi.      The  nerve  termi- 
nates in  the  wall  of  the  blood-ves- 
sels  and  has  no  connection   with  the   bone  cells. 
Haversian  systems  occupy  a  central  zone  in  a  bony 
shaft.     External  and  internal  to  this  zone  compact 
lamellae  are  present,  arranged  parallel  to  the  surface. 


Fig.  47. —  Bone 
cell  or  corpuscle. 
The  cell  occupies  a 
lacuna. 


TISSUES. 


Outer  circumferen- 
tial lamella. 


,  -- ' — 

I 

/    „_' — „  Haver  sian  or  con* 

,          -       .     ^m,      >r    >     |  centric  lamella. 


/  /        \     •*• 

« 


'    /  t 

:  x ' 


:>      '  x  I 

«.   v        •*>    "„     -'-    (•'    »  .    v  v  "rf          Interstitial  l 

'  •<•-  — „ t-^t— '-*— Sr-V-.--f: 


wwer  circumferen- 
tial lamella. 


Fig  48 — Segment  of  a  transversely  ground  section  from  the  shaft 
of  a  long  bone,  showing  all  the  lamellar  systems.  Metacarpus  of  man 
(Bohm  and  Davidoff). 


80       NORMAL  HISTOLOGY   AND   ORGANOGRAPHY, 

In  the  circumferential  lamellae  canals,  called  Volk- 
manris  canals,  convey  blood-vessels  to  the  Haver- 
sian  canals.  In  the  angular  interstices,  between  the 
Haversian  systems,  lamellae  and  canaliculi  are  found 
arranged  like  those  of  the  circumferential  lamellae. 
The  shafts  of  long  bones  contain  a  marrow  cavity. 
At  the  ends  the  marrow  cavity  disappears,  and  the 
bony  structure  becomes  spongy  with  many  inter- 
stices and  is  then  called  cancellate  bone.  The  middle 
of  flat  bones  is  made  up  of  a  like  loose  structure 
called  diploe. 


Haversian  canal.  .. 


Fig.  49. — Portion  of  a  transversely  ground  disc  from  the  shaft  of  a 
human  femur  (Bohm  and  Davidoff). 

Periosteum. — The  periosteum  is  a  dense,  fibrous, 
connective-tissue  membrane  that  covers  the  bone 
and  is  derived  from  the  perichondrium  of  the  carti- 
lage. It  is  composed  of  two  layers,  (a)  an  inner 
layer  that  contains  many  elastic  fibers  and  osteo- 
blasts,  or  bone-forming  cells,  known  as  the  osteo- 
genetic  layer,  and  (b)  an  outer  layer  of  coarse, 
white,  fibrous  bundles  where  numerous  blood-vessels 
ramify  and  send  branches  to  the  Haversian  canals. 


TISSUES.  gj 

The  periosteum  is  anchored  to  the  compact  bone  by 
means  of  bundles  of  fibers  (Sharpey's  fibers)  that 
pass  concentrically  or  parallel  to  the  Haversian 
systems. 

Blood  Supply o — The  compact  bone  is  supplied 
with  blood  from  the  periosteum.  Larger  blood- 
vessels, called  perforating  vessels,  pass  directly 
through  the  bony  shaft  and  supply  the  marrow. 
In  removing  bone,  as  a  rib,  the  periosteum  is  not 
taken  away,  and  because  of  the  latter 's  vascularity 
and  osteogenetic  layer,  the  removed  part  regenerates. 
On  the  other  hand,  infected  marrow  and  diseased 
bone  may  be  removed  from  the  inner  surface  until  a 
mere  shell  remains  of  the  once  solid  shaft.  If  all 
the  infection  is  removed  a  regeneration  follows. 

Development  of  Bone. — The  development  of  bone 
is  either  intramembranous  or  endochondral.  In  the 
latter  a  cartilage  stage  intervenes,  otherwise  the 
history  in  each  case  is  the  same.  A  synopsis  of 
endochondral  development  is  as  follows: 

1 .  A  solid  shaft  of  hyaline  cartilage,  non-vascular 
and  without  any  marrow  cavity. 

2.  In  the  center  of  this  shaft  the  cartilage  cells 
enlarge,  their  lacunae  enlarge  and  coalesce,  particu- 
larly along  lines  extending  toward  the  ends  of  the 
bone.     The  rosette  produced  by  this  excavation  is 
called  the  primary  areola  of  Sharpey. 

3.  Lime  salts  are  deposited  in  the  thin  walls  of 
these  spaces,  making  calcified  cartilage. 

4.  Osteogenetic  cells  and  blood-vessels  from  the 
periosteum  enter  the  cartilage  spaces.     The  carti- 
lage cells  disappear  with  this  invasion  and  the  ex- 


82        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

cavation,  begun  by  the  cartilage  cells,  is  -further  en- 
larged by  the  bone  cells.  The  excavated  areas  are 
now  called  the  secondary  areolce  of  Sharpey,  the 
cavities  having  a  rich  blood  supply  quite  in  con- 
trast with  the  primary  areolae.  The  marrow  cavity 


Vesicular  cartilage  cells* 

Primary  periosteal  bone 
lamella. 

Periosteal  bud. 


Periosteum. 


Unaltered  hyaline 
cartilage. 


Fig.  50. — Longitudinal  section  through  a  long  bone  (phalanx) 
of  a  lizard  embryo.  The  primary  bone  lamella  originating  from  the 
periosteum  is  broken  through  by  the  periosteal  bud.  Connected  with 
the  bud  is  a  periosteal  blood-vessel  containing  red  blood-corpuscles 
(Bohm  and  Davidoff). 

is  excavated  and  the  shaft  becomes  longitudinally 
porous.  Endochondral  bone,  therefore,  develops  in 
cartilage,  not  from  cartilage. 

5 .  Osteogenetic  cells  attach  themselves  to  the  wall 
of  these  enlarged  Haversian  canals  and  become  en- 
closed in  lime  deposits,  forming  thus  the  outer  lam- 
ellae and  outer  row  of  bone  cells  of  each  Haversian 


TISSUES. 


system.     Cells  with  lamellae  are  added  centripetally 
to  this  outer  row  and  thus  ultimately  complete  the 
Haversian  system,  leaving   a 
small  central  canal  contain- 
ing vessels  and  a  nerve. 

Ossification  begins  in  the 
center  of  the  cartilage  shaft 
and  proceeds  gradually 
toward  each  end,  so  that  all 
the  above  changes  occur  at 
one  and  the  same  time. 
After  birth  these  changes  go 
on  at  the  ends  of  the  bone, 
so  long  as  it  keeps  growing. 
During  this  period  the  bone 
is  made  thicker  by  deposits 
from  the  periosteum  forming 
the  circumferential  lamellae  of 
bony  shafts.  These  lamellae 
are  added  without  the  inter- 
vention of  a  cartilage  stage 
and  therefore  represent  intra- 
membranous  development. 

Regeneration  of  Bone.— 
The  embryonic  process  of 
developing  bone  is  repeated 
every  time  a  broken  bone 
heals.  As  a  rule  the  carti- 
lage stage  does  not  intervene. 

*  •  r        1         11-  Fig.  51.— Longitudinal 

A     SynopSIS     Of     the     healing        section    through    area   of 
r»rrv>pQQ   nf    a     Qirnnlp    frartnrp        ossification      from      long 

bone   of  human   embryo 
IS  as  follows:  (Huber). 


84        NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

1.  Hemorrhage  and  clot.     The  fibrin  of  the  clot 
tends  to  hold  the  broken  ends  in  apposition.     The 
parts  are  swollen  and  red,  due  to  the  influx  of  blood 

2.  Organization  .of    the    clot.     Connective- tissue 
cells  and  white  corpuscles  enter  the  clot,  feed  upon 
it  and  ultimately  replace  it,  the  connective-tissue 
cells  meanwhile  producing  fibers.     The  organized 
clot  is  a  more  substantial  fabric  and  more  firmly 
holds  the  broken  ends  in  apposition. 

3.  Osteogenetic  cells  enter  the  organized  clot  anc 
deposit  lime  salts,  producing  a  primary  callus.     The 
connective  fibers  shrink,  pulling  the  broken  ends 
firmly  together,   producing  a  sensation  knowrn  as 
knitting  of  bone.     The  primary  callus  surrounds  the 
bone,  and  may  even  fill  the  marrow  cavity. 

4.  Haversian   systems   are   formed,    uniting   the 
broken  ends.     These    systems    appear  just  as    de- 
scribed under  development  of  bone. 

5.  Primary  callus  is  absorbed  and  marrow  cavity 
excavated.     Bone  cells  called   osteoclasts  are   sup- 
posed to  be  active  factors  in  this  absorption. 

General  Considerations. — Bone  does  not  grow  in 
the  same  sense  as  other  tissues  do.  Any  increase  in 
size  is  due  to  apposition  of  bone  lamellae  upon  those 
already  formed.  Accompanying  and  often  pre- 
ceding bone  production  we  usually  find  a  destructive 
or  excavating  process.  It  is  believed  two  classes  of 
cells  bring  about  these  changes :  (a)  Osteoclasts  that 
cause  bone  absorption,  and  (b)  osteoblasts  that  en- 
gage in  bone  production.  The  latter  are  supposed 
to  be  particularly  abundant  in  the  osteogenetic 
layer  of  the  periosteum. 


TISSUES.  85 

Bone  tumors  are  not  uncommon  and  are  called 
osteoma.  They  are  of  slow  growth,  usually  as- 
sociated with  bone,  and  harmless. 

On  account  of  the  great  vascularity,  a  broken  bone 
heals  more  rapidly  than  a  broken  tendon,  or  liga- 
ment, or  a  broken  cartilage.  An  old  bone  is  brittle 
and  the  healing  process  a  slow  one  on  account  of  the 
increase  of  earthy  matter  and  a  decrease  of  the 
organic. 

An  infection  beneath  the  periosteum  is  a  felon. 
The  periosteum  is  firmly  attached  to  the  bone  by 
Sharpey's  fibers  and  the  pressure  produced  by  an  in- 
fection beneath  it  gives  rise  to  extreme  pain,  which 
is  instantly  relieved  by  an  incision.  An  inflam- 
mation in  the  bone  is  called  an  ostitis,  while  if  it  is 
located  in  the  marrow  cavity  it  is  called  an  osteo- 
myelitis. 

III.  MUSCULAR  TISSUE. 

Muscular  tissue  consists  of  elongated  cellular  ele- 
ments in  which  contraction  takes  place  along  the 
long  axis  of  the  cell.  This  contraction  is  intrinsic  to 
the  muscle  cytoplasm,  and  of  this  the  spongioplasm 
seems  to  be  the  active  agent.  The  word  sarcode  and 
its  derivatives  is  used  in  describing  muscle  proto- 
plasm. This  word  was  introduced  by  Dujardin,  in 
1835,  and  was  later  replaced  by  the  word  protoplasm. 

i.  Smooth,  Non-striated  or  Involuntary  Muscle. — 
This  is  the  simplest  form  of  muscle  tissue.  The  cells 
are  mononucleated,  elongated,  or  spindle-shaped, 
and  vary  in  length  from  40  to  200  />«.  The  nucleus 
occupies  the  center  of  the  cell,  is  rich  in  chromatin, 
and  oval,  with  blunt  ends,  or  cigar-shaped.  The 


86       NORMAL   HISTOLOGY   AND   ORGANOGRAPHV. 

cytoplasm  is  longitudinally  striated,  the  striations 
being  due  to  fibrils  or  sarcostyles,  which  are,  structur- 
ally, probably  analogous  to  the  spongioplasm. 
Between  the  fibrils  there  is  a  homogeneous  sub- 
stance, the  sarcoplasm,  which  is  analogous  to  the 
hyaloplasm.  These  cells  are  enclosed  in  a  delicate 
cement  layer  usually  not  described  as  a  cell  wall,  and 
in  which  a  fine  interlacing  reticulum  has  recently 
been  described.  The  ends  overlap  each  other  and 
are  held  together  by  a  delicate  cement  substance. 
Nerve-fibers  from  the  sympathetic  nervous  system 
reach  the  muscle  cells  and  terminate  in  small  gran- 
ules upon  the  muscle  cytoplasm. 

Nucleus 


Nucleus 


Artery 


Vein. 


Fig.  52. —  a,  Cell  from  smooth  muscle  of  intestine;  b,  Cross  section  of 
smooth  muscle  of  intestine. 

Smooth  muscle  is  found  in  the  wall  of  the  tubes  of 
the  body,  and  invariably  in  thin  layers,  with  one 
exception — the  wall  of  the  uterus — where  the  muscle 
may  be  an  inch  in  thickness.  Usually,  too,  this 
muscle  is  laid  down  as  an  internal  circular  layer 
with  an  externally  applied  and  thinner  longitudinal 
layer.  Plain  muscle  is  found  in  the  wall  of  the  ali- 
mentary tract,  trachea  and  bronchi,  bladder,  ureter, 
uterus,  Fallopian  tubes,  urethra, .  vas  deferens, 


TISSUES. 


blood-vessels,  lymph- vessels,  large  ducts  of  glands, 
nipple,  hair-follicles,  Eustachian  tube,  spleen,  pros- 
tate gland,  ciliary  muscles,  and  iris  of  the  eye. 

2.  Cardiac  Muscle. — The  heart  ontogenetically  is 
a  modified  blood-vessel,  and  its  muscle,  therefore, 
has   the   same   origin   as   smooth   muscle.     Heart 
muscle  cells  are  oval  or  brick-shaped  and  mono- 
nucleated,  the  oval  nuclei  occupying  the  center  of 


Muscle  nucleus. 


Connective-tissue  cell. 


pig,  23.  —  Longitudinal  section  of  heart  muscle  fibers. 

the  cell.     Longitudinal  fibrils  and,   in  addition,   a 

fine  cross  striation,  are  present  in  the  cytoplasm, 

resembling  the  cross  stri- 

ation of  voluntary  mus- 

cle.   This  cross  striation 

is  explained  under  Vol- 

untary    Muscle,     and 

therefore    will    not    be 

given    here.     The   cells 

are  joined  together,  end 

to  end,  by  delicate  ce- 

ment  lines  and  laterally 

may  unite  with  adjacent  cells  by  means  of  protoplas- 

mic processes.     In  the  cytoplasm  adjacent  to  the  ends 

of  the  nuclei,  normally  fat  is  frequently  present  and 


Muscle  nucleus. 


Fig 


54_Cross  section  of  heart 
muscle  fibers- 


88        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

also  some  pigment.  The  latter  is  more  prominent  in 
old  hearts,  to  which  it  imparts  a  brown  color. 

At  present  the  exact  structure  of  the  heart  muscle 
is  a  disputed  question.  In  sections,  many  breaks 
or  artifacts  resemble  the  cement  lines  separating 
adjacent  cells.  The  longitudinal  fibrils  are  said  to 
penetrate  the  cement  and  thus  establish  a  con- 
tinuity of  protoplasm  between  adjacent  cells.  The 
presence  or  absence  of  a  cell  wall,  analogous  to  the 
sarcolemma  of  voluntary  muscle,  is  also  disputed. 

3.  Voluntary  Muscle. — A  voluntary  myscle  fiber 
is  a  multinucleated,  greatly  elongated  cell,  which 
may  attain  a  length  of  12  cm.  (5  inches).  These 
fibers  are  arranged  parallel  to  each  other  and  grouped 
into  bundles,  called  fasciculi.  Each  fasciculus  is 

Sarcolemma. 


Sarcostyles. 


Fig-  55- — Voluntary  muscle  fiber.     The  sarcoplasm  has  broken,  show- 
ing the  smooth  sarcolemma. 

surrounded  by  connective-tissue  cells  and  fibers  in 
which  many  blood-vessels  ramify.  A  finer  fabric  of 
connective  tissue  penetrates  the  fasciculus  and  gives 
support  to  the  individual  fibers.  The  connective 
tissue  that  enters  a  fasciculus  is  called  the  endo- 
mysium,  and  that  which  surrounds  a  fasciculus  is 
called  the  perimysium.  Fasciculi  are  grouped  into 
coarser  bundles  and  these  collectively  make  up  a 
muscle.  The  muscle  is  in  turn  enveloped  in  a  firm 
connective -tissue  layer  called  the  epimysium.  In 
gross  anatomy  the  latter  constitutes  the  deep  fascia 


TISSUES.  89 

of  muscle.  In  tough  meat  the  connective-tissue 
element  is  extensively  developed  and  the  fasciculi 
are  large  and  coarse. 

Each  muscle  fiber  has  a  delicate,  transparent, 
smooth  cell  wall  called  the  sarcolemma.  The  oval 
distinct  nuclei  lie  immediately  beneath  the  sarco- 
lemma in  higher  vertebrates,  but  in  lower  forms  and 
in  all  embryos  the  nuclei  lie  deeper  in  the  muscle 
protoplasm.  These  nuclei  have  the  same  structure 
as  the  nuclei  of  any  other  tissue,  but  the  cytoplasm 
shows  a  distinct  and  regular  cross  and  longitudinal 
striation,  characteristic  of  only  one  other  tissue — 
the  cardiac  muscle.  The 
longitudinal  striation  is  /ik  4jij$i&^cohnheim>s 

fa&f, ;  ,\  |W ;_>; ,  •S-.-.^-jA  area,  a  bundle 

due  to  the  presence   of      M  Itg]       of  sarcostyles. 

j    i-  £i-ii  11    J        /  31 — Sarcoplasm. 

delicate     fibrillae     called     %  ^M 

sarcostyles,  which  is  an-      ^/^^^ 

alogOUS    tO     the     SpOngio-  pfl^W\ Muscle  nucleus. 

plasm  of  other  cells.     A  %il|8l 

.,  i  v-vVf'-^'y^'    "*  Sarcolemma. 

more  homogeneous   and  ^jSf® 

fluid  substance  intervenes  ^w 

between    the  SarCOStyleS,       Fig.  56.— Cross   section    of   three 
n     1  ,  7  ...  voluntary  muscle  fibers. 

called  sarcoplasm,  and  is 

in  turn  analogous  to  the  hyaloplasm  of  other  cells. 
The  sarcostyles  are  not  uniformly  or  evenly  dis- 
tributed in  each  muscle  fiber,  but  are  grouped  into 
bundles.  In  cross  sections  the  fiber  has  therefore 
a  honeycomb  structure,  the  minute  areas  being 
known  as  Cohnheim's  fields.  A  single  Cohnheim 
field  represents  the  cut  ends  of  a  single  bundle  of 
fibrils  or  sarcostyles. 

The  cross  striation  is  intricate  and  therefore  more 
difficult  to  explain.     This  striation  consists  of  alter- 


9° 


NORMAL  HISTOLOGY  AND  ORGANOGKAPHY. 


nating  light  and  dark  bands.  The  dark -bands  are 
doubly  refractive  to  light,  or  anisotropic,  while  the 
light  bands  are  singly  refractive,  or  isotropic.  The 
dark  bands  represent  a  predominance  of  the  sarco- 
style  substance,  and  the  light  bands  a  predominance 
of  the  sarcoplasm.  In  the  middle  of  the  light  band 
a  dark  line  can  be  seen,  known  as  Krause's  membrane. 
In  the  middle  of  the  dark  band  a  light-colored  line  is 
present,  known  as  Hensen's  median  disc.  The  latter 
disappears  when  a  fiber  contracts. 


KtW 


Sarcomere. 


—  Hensen's  me- 
dian disc. 


Fig.   57. — Diagram  of  voluntary  muscle  fiber;   A,  Fiber  relaxed;    B, 
fiber  contracted. 

These  transverse  markings  are  all  due  to  the  dis- 
tribution of  the  sarcoplasm  and  the  regular  con- 
strictions of  the  sarcostyles.  The  sarcostyles  are 
not  of  uniform  dimensions,  but  at  regular  intervals 
show  dilatations  alternating  with  constrictions.  The 
dilatations  appear  at  regular  intervals  and  in  the 
same  transverse  plane  of  the  muscle  fiber,  thus 
giving  rise  to  the  dark  band.  Krause's  membrane 
is  not  a  membrane,  but  represents  minute  nodal 
points  of  the  sarcostyles,  placed  in  the  same  trans- 


TISSUES. 


Muscle. 


verse  plane  of  the  fiber  and  in  the  middle  of  the  light 
band.  The  light  band  represents  an  abundance  of 
sarcoplasm  and  it  is  in  this  sectional  area  that  the 
sarcostyles  suffer  a  constriction.  As  Hensen's  me- 
dian disc  is  a  light  line  in  the  middle  of  the  dark 
band  there  must  be 
a  deep  constriction, 
if  not  a  complete 
constriction  of  the 
sarcostyles  at  this 
point. 

The  whole  muscle 
fiber  between  the 
two  Krause's  mem- 
branes is  called  a 
sarcomere,  and  con- 
sists of  a  median 
dark  band  and  the 
proximal  halves  of 
the  adjacent  light 
bands.  A  single 
fibril  or  sarcostyle 
between  two  of 
Krause's  mem- 
branes is  called  a 
sarcous  element. 

It  is  believed  that 
muscular  contractil- 
ity is  particularly  a  function  of  the  sarcostyles  and 
that  the  sarcoplasm  serves  more  as  a  storage  of  energy 
or  food.  As  to  color  there  are  two  kinds  of  muscle, 
white  and  red.  In  white  meat,  as  the  muscle  of  the 


Tendon. 


Fig.  58. — Part  of  a  longitudinal  sec- 
tion through  the  line  of  junction  be- 
tween muscle  and  tendon.  At  the  line 
where  the  tendon  fibrils  join  the  sarco- 
lemma  (a),  the  nuclei  of  the  muscle  are 
very  numerous.  Sublimate  preparation 
(Bohm  and  Davidoff). 


92        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

breast  of  a  bird,  the  fibers  have  a  poor  supply  of 
sarcoplasm  and  a  predominance  of  sarcostyles.  In 
red  meat  the  fibers  are  rich  in  sarcoplasm  and  have  a 
less  supply  of  the  sarcostyle  protoplasm.  In  the 
myology  of  man  both  kinds  of  fibers  are  present. 
The  white  fibers  are  more  powerful  but  have  less 
endurance;  that  is,  if  held  in  tetanic  contraction 
with  no  interval  of  rest  they  would  tire  quicker  than 
the  red  fibers.  The  pectoral  muscle  of  birds  is 
powerful,  but  would  soon  tire  but  for  the  interval 
of  rest  that  intervenes  between  the  strokes  of  the 
wing;  that  is,  during  its  upward  movement. 


Fig-  59- — Three  voluntary  muscle  fibers  from  an  injected  muscle,  show- 
ing network  of  blood-capillaries. 

Blood  Supply. — Blood-vessels  follow  the  con- 
nective tissue  of  a  muscle,  and  penetrate  to  the 
individual  fibers  where  they  break  up  into  capil- 
laries. These  vessels  run,  as  a  rule,  parallel  to  the 
fibers,  forming  a  network  with  anastomosing 
branches.  They  extend  in  a  varicose  manner 
between  the  fibers  in  such  a  way  that  when  a  muscle 
contracts  they  readily  adjust  themselves,  without 
breaking. 

Nerve  Supply. — Medullated  nerve  fibers  accompany 


TISSUES.  93 

the  blood-vessels  and  terminate  beneath  the  sarco- 
lemma  in  special  end  plates  called  muscle  plates. 
These  will  be  described  under  special  nerve  endings. 
Non-medullated  or  sympathetic  nerve  fibers  also 
accompany  blood-vessels,  but  they  innervate  the  in- 
voluntary musculature  of  arteries  and  veins. 

Distribution. — Voluntary  muscles  are  the  skeletal 
muscles,  and  make  up  the  bulk  of  the  body. 
Striated  fibers  are  present  in  the  upper  part  of 
the  esophagus,  and  also  constitute  the  platysma 
muscle  of  the  skin. 

Union  with  Tendon  and  Bone. — The  muscle 
fibers  terminate  abruptly  with  tendon  fibers.  This 
is  not  a  direct  end-to-end  union,  but  the  tendon 
fibers  fuse  with  the  sarcolemma  at  an  angle.  In  the 
same  way  the  muscle  fibers  unite  with  the  periosteum 
of  the  bone.  At  this  point  Sharpey's  fibers  are 
particularly  abundant  and  firmly  anchor  the  peri- 
osteum to  the  compact  bone  lamellae. 

General  Considerations. — A  muscle  tumor  is  called 
a  myoma.  Tumors  of  plain  muscle  are  common  in 
the  wall  of  the  uterus.  They  are  benign,  of  slow 
growth,  and  usually  harmless.  A  tumor  of  striated 
muscle  fibers  is  very  rare.  The  tissue  is  highly 
specialized  and  the  fibers  therefore  do  not  multiply 
readily.  If  a  muscle  is  injured  or  cut  the  voluntary 
fibers  regenerate  partly  from  the  cut  end  and  partly 
from  free  muscle  nuclei  that  are  shed  into  the  wound, 
but  mostly  by  connective-tissue  repair  that  leaves  a 
permanent  scar. 

The  physiological  action  of  plain  muscle  is  slow, 
producing  peristaltic  contractions.  That  of  volun- 
tary muscle  is  rapid,  as  in  the  wings  of  insects. 


94        NORMAL   HISTOLOGY   AND  ORGANOGRAPHY. 

Voluntary  muscles,  while  more  powerful,  tire  easily. 
Plain  muscle  has  a  wonderful  endurance.  The 
pain  produced  by  violent  action  of  plain  muscle  is 
in  direct  proportion  to  the  degree  of  contraction. 
Some  examples  are :  the  colicky  pains  of  the  intestine ; 
labor  pains ;  pains  due  to  calculi  in  the  ureter  or  bile 
duct;  or  the  pain  in  appendicitis  produced  by  con- 
traction of  the  plain  muscle  of  the  appendix.  These 
pains  have  many  things  in  common  They  may 
last  for  hours,  they  remit  and  recur  with  regularity, 
and  they  come  in  waves. 

An  infection  in  a  muscle,  as  a  psoas  abscess,  bur- 


Telodenc 
Nucleus  and  nucleolus. 

Neurilemma .  M  edullary  sheath . 


I 
Axis  cylinder.  Node  of  Ranvier. 


Fig.  60. — Diagram  of  a  neuron. 

rows  in  the  fascia, — that  is,  spreads  along  the  con- 
nective-tissue septa,  perimysium  and  endomysium. 
The  quality  of  meat  depends  on  the  amount  of  con- 
nective tissue.  In  tough  meat  the  fasciculi  are 
coarse  and  perimysium  abundant.  In  tender  sir- 
loin the  reverse  prevails. 

IV.    NERVOUS  TISSUE. 

Nervous  tissue  is  most  highly  specialized  of  all 

tissues  and  consists  of  elements  called  neurons.     A 

neuron  is  a  nerve  cell  with  all  its  processes.     These 

cells  vary  greatly  in  size;  usually  they  are  large. 


TISSUES.  95 

They  have  one  or  more  processes,  no  cell  wall,  and  a 
distinct  nucleus.  The  nucleus  has  a  conspicuous 
nucleolus,  a  prominent  nuclear  membrane,  but  a 
small  supply  of  chromatin. 

The  cytoplasm  is  usually  pigmented,  the  pigment 
being  collected  to  one  side  of  the  cell.  It  is  this 
pigment  that  gives  nervous  tissue  a  gray  color 
wherever  these  cells  are  found.  Fat  and  vacuoles 
are  also  usually  found  in  the  cytoplasm.  The  proc- 
esses of  nerve  cells  are : 


Connective  ... 
tissue. 


Fibrils  of  axial 
cord. 


Fig.  61. — Transverse  section  through  the  sciatic  nerve  of  a  frog. 
At  a  and  b  is  a  diagonal  fissure  between  two  Lantermann's  segments; 
as  a  result,  the  medullary  sheath  here  appears  double  (Bohm  and 
Davidoff). 

i.  Axis  cylinder  (Deiters'  process,  axon,  neurite, 
or  neuraxon),  which  is  usually  a  long  protoplasmic 
process  that  physiologically  carries  an  impulse  away 
from  the  cell.  Collaterals  are  nerve  processes  that 
leave  the  axis  cylinder  at  right  angles.  They  are 
commonly  found  near  the  nerve  cells,  but  may  ap- 
pear at  a  node  of  Ranvier  some  distance  away  from 
the  nerve  cell. 


96       NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

2.  Dendrites,  which  are  usually  short  processes, 
very  much  branched,  and  physiologically  carry  an 
impulse  toward  the  nerve,  cell.  A  collection  of 
nerve  cells  constitutes  a  ganglion,  while  a  nerve 
plexus  is  a  reticulum  or  interlacing  of  nerve  fibers. 
Nerve  cells  are  classified,  according  to  the  number 
of  their  processes,  into  unipolar,  bipolar,  and 
multipolar. 

Nerve  Cells. — i.  Unipolar  nerve  cells. — These  are 
nerve  cells  with  but  one  process.  If  a  nerve  cell 


Pat  cells. 


Artery  and  vein.  Bipolar  nerve  cells. 

Fig.  62. —  Section  of  spinal  ganglion. 

has  but  one  process  that  process  must  be  an  axis 
cylinder.  If  a  nerve  cell  has  many  processes  onl} 
one  is  an  axis  cylinder,  the  others  are  dendrites. 
Unipolar  nerve  cells  are  found  in  the  olfactory  mucous 
membrane.  They  are  columnar  or  cylindrical  and 
each  gives  rise  to  a  basal  process,  the  axis  cylinder, 
which  remains  non-medullated  and  extends  through 
the  cribriform  plate  to  enter  the  olfactory  lobe  of  the 
cerebrum.  This  class  of  nerve  cells  is  common  ir 
invertebrates. 


TISSUES. 


97 


2.  Bipolar  Nerve  Cells. — Bipolar  nerve  cells  have 
two  processes, — one  axis  cylinder  and  one  dendrite. 
Nerve  cells  of  the  spinal  ganglia  and  ganglia  of  the 


Nerve  fibers  in  cross  section. 


Nucleus  of  nerve 
cell. 

Nucleolus. 


Connective-tissue  cells  forming  a  capsule 
around  the  nerve  cell. 

Fig.  63. — Two  bipolar  nerve  cells  from  the  spinal  ganglion. 

cranial  nerves  belong  to  this  class.  These  cells 
apparently  are  unipolar,  but  their  embryology 
clearly  shows  the  single  process  to  be  morphologically 
equivalent  to  two.  In 
this  particular  case 
the  long  peripheral 
process  carries  an  im- 
pulse to  the  cell,  and 
this  long  process  is 
therefore  a  dendrite. 
The  short  process  that 
unites  the  ganglion 
with  the  central  ner- 
vous system  is  the 
axis  cylinder.  These 
large  bipolar  cells  are 


Fig.  64. — Three  ganglion  cells  from 
a  spinal  ganglion  of  a  rabbit  embryo. 
The  cells  are  still  bipolar.  Their  proc- 
esses come  together  in  later  stages, 
and  finally  form  the  T-shaped  structure 
seen  in  the  adult  animal;  chrome-silver 
method  (Bohm  and  Davidoff). 


surrounded  by  a  cap- 
sule of  connective-tissue  cells.  The  cells  are  large  and 
the  single  compound  process  very  soon  divides  into 
the  two  processes  mentioned  above.  The  cytoplasm 

7 


98        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

of  these  cells  has  a  fibrillar  structure,  this  striation 
having  a  close  relation  to  the  fibrillae  of  the  axis 
cylinder. 

The  spinal  ganglia  are  situated  on  the  posterior 
or  sensory  root  of  the  spinal  nerves  and  within  the 
vertebral  canal.  The  Gasserian,  geniculate,  audi- 
tory, jugular,  and  petrosal  ganglia  of  the  cranial 
nerves  are  morphologically  equivalent  structures. 
The  nerve  cells  of  all  these  ganglia 
are  bipolar,  with  the  exception  of  a 
few  cells  said  to  be  multipolar.  In 
addition  to  nerve  cells,  nerve  fibers 
and  connective  -  tissue  elements 
make  up  the  histology  of  these  gan- 
glia. A  liberal  blood  and  lymph 
supply  is  always  present. 

3.  Multipolar  Nerve  Cells.— 
These  are  nerve  cells  with  many 
processes,  only  one  of  which  is  an 
axis  cylinder.  They  constitute  by 
far  the  bulk  of  nerve  cells  and  are 
found  in  the  brain  and  spinal  cord 
and  in  ganglia  along  the  sympa- 
thetic nervous  system.  The  cells 
vary  in  size  from  4  ^  in  the  granular 
layer  of  the  cerebellum  to  150  //,  the  largest  nerve 
cells  of  the  spinal  cord.  Chromatophile  granules, 
vacuoles,  fat,  and  a  fibrillar  structure  is  found 
associated  with  the  cytoplasm.  Large  multipolar 
nerve  cells,  called  cells  of  Purkinje,  are  found  in  the 
cerebellum  and  will  be  described  with  the  histology 
of  that  organ. 


Nucleus, 


Fig.  65.  — Gan- 
glion cell  with  a 
process  dividing  at 
a  (T-shaped  proc- 
ess); from  a 
spinal  ganglion  of 
the  frog  (Bohm 
and  Davidoff). 


TISSUES. 


99 


Nerve  Fibers. — i.  Medullated  Fibers. — Medullated 
nerve  fibers  usually  consist  of  three  parts,  (a)  axis 
cylinder,  (6)  medullary  sheath,  (c)  neurilemma.  An 
axis  cylinder  is  a  cell  process  that  carries  an  impulse 
away  from  the  nerve  cell.  It  is  a  slender  cytoplasmic 
process  and  may  be  very  long,  as  is  the  case  with 


Fig.  66. — Ganglion  cell  from  the  Gasserian  ganglion  of  a  rabbit;  stained 
in  methylene-blue  (intra  vitani)  (Huber). 

the  motor  fibers  that  come  from  nerve  cells  in  the 
anterior  horn  of  the  spinal  cord  and  extend,  without 
interruption,  to  muscles  in  the  distal  parts  of  the 
limbs.  The  axis  cylinder  presents  a  longitudinal 
striation,  a  fibrillar  structure,  that  is  supposed  to  be 
continuous  with  the  cytoplasmic  striation  of  the 


100       NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 


Dendrite.       Neuraxis. 


'Neuraxis. 


Dendrite. 


Fig.  67. — Motor  neurons  from  the  anterior  horn  of  the  spinal  cord  o! 
a  new-born  cat;    chrome-silver  method  (Huber). 


'-n-n-  Telodendrwn. 


Dendrite. 


Cell-body. 


Neuraxis. 


Fig.  68. — A  nerve  cell  with  branched  dendrites  (Purkinje's  cell), 
from  the  cerebellar  cortex  of  a  rabbit;  chrome-silver  method  (Bohni 
and  Davidoff). 


TISSUES. 


101 


cell  body.  The  fibrils  are  imbedded  in  a  fluid  pro- 
toplasmic substance,  the  neuroplasm,  and  the  whole 
surrounded  by  a  delicate  membrane,  the  exolemma. 
Implantation  cone  is  an  elevation  that  is  sometimes 


Brush-like  telodendrion. 


Main  dendrite.  — 


Secondary  dendrite,  - 


Basal  dendrite. 


Neuraxis  with  collaterals. 


Fig.  69. — Pyramidal  cell  from  the  cerebral  cortex  of  man;    chrome- 
silver  method  (Bohm  and  Davidoff). 

present  at  the  junction  of  the  axis  cylinder  and  cell 
body. 

The  medullary  sheath  (white  sheath  of  Schwann) 
is  a  covering  to  the  axis  cylinder.    This  sheath  never 


102     NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 


extends  to  the  nerve  cell  but  begins  a  little  distance 
from  it.  It  consists  of  fat  and  neurokeratin.  The 
latter,  on  burning,  gives  an  odor  of  burnt  bone.  It 


Ranvier's  node. 

Axial  cord. 

-»  Medullary  sheath. 


Nucleus. 


Ranvier's  node. 


Fig.  70.— Medullated  nerve  fibers  from  a  rabbit,  varying  in  thick- 
ness and  showing  internodal  segments  of  different  lengths.  In  the  fiber 
at  the  left  the  neurilemma  has  become  slightly  separated  from  the  under- 
lying structures  in  the  region  of  the  nucleus  (Bohm  and  Davidoff). 

is  this  sheath  that  gives  the  white  color  to  nerves  and 
the  white  matter  of  the  brain.  In  osmic  acid  prep- 
arations, oblique  fissures  appear  in  the  medullary 
sheath  dividing  it  into  sections  known  as  Schmidt- 


TISSUES, 


103 


—  Fibrils  of  axial 
cord. 

Neurilemma. 


—  Segment  of 
Lantermann. 


Lantermann  segments.  It  is  claimed  by  some  that 
these  are  artifacts.  Nodes  of  Ranvier  are  con- 
strictions of  this  sheath  at  regular  intervals  of  80 
to  900  ft.  The  smaller  the  fiber,  the  greater  the 
distance  between  these  nodes.  Long  fibers  are 
slender,  with  long  distance  between  the  nodes; 
short  fibers  are  coarse,  with 
short  distance  between  the 
nodes.  Furthermore,  in  young 
fibers  and  at  the  distal  por- 
tion of  nerve  fibers  the  nodes 
are  relatively  closer  together. 

The  neurilemma  is  a  thin 
structureless  membrane  that 
surrounds  the  medullary 
sheath.  An  oval  nucleus  is 
present  in  this  sheath,  midway 
between  the  nodes  of  Ranvier. 
At  each  node  the  neurilemma 
is  constricted  and  touches  the 
axis  cylinder,  which  in  turn 
may  be  slightly  thickened  at 
this  point  and  may  give  off  a 
collateral.  Medullated  nerve 

fibers  with  a  neurilemma  are  found  in  the  cranial 
and  spinal  nerves.  Medullated  fibers  without  a 
neurilemma  are  found  in  the  brain  and  spinal  cord. 
The  neurilemma  gives  great  strength  to  the  fibers. 
Its  absence  in  the  brain  and  cord  accounts  for  the 
pulpy,  soft  nature  of  this  tissue. 

2.  Non-medullated  nerve  fibers  with  a  neurilemma, 
but  without  a  medullary  sheath,  mingle  with  the 
medullated  fibers.  The  sympathetic  system  con- 


Fig.  71. —  Longitudinal 
section  through  a  nerve 
fiber  from  the  sciatic  nerve 
of  a  frog  (Bohm  and 
Davidoff). 


104      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 


sists  largely  of  non-medullated  fibers.  Terminal 
branched  endings  of  an  axis  cylinder,  called  neuro- 
podia,  have  neither  medullary  sheath  nor  neurilemma. 
The  axis  cylinder,  just  as  it  leaves  its  nerve  cell,  is 
likewise  uncovered. 

Nerve  Trunk. — The  fibers  that  constitute  a  nerve 
are  grouped  into  bundles  called  funiculi.  Each 
funiculus  is  enclosed  in  a  connective- 
tissue  sheath,  the  perineurium,  which 
sends  septa,  the  endoneurium,  in 
among  the  individual  fibers.  The 
whole  nerve  is  enclosed  in  a  firm  con- 
nective-tissue sheath,  the  epineurium. 
Blood-  and  lymph- vessels  accompany 
the  connective-tissue  elements  and 
ramify  through  the  nerve  just  as  is 
the  case  in  a  muscle. 

Nerve  cells  with  a  long  axis  cylinder 
were  classified  by  Golgi  as  Type  I,  and 
with  a  short  axis  cylinder  as  Type  II. 
Golgi  believed  the  former  to  be  motor 
in  function,  and  the  latter  sensory,  a 
classification  no  longer  tenable. 

Neuroglia  tissue  is  a  delicate  sup- 
porting tissue  of  the  brain  and  cord, 
consisting  of  cells  with  many  fine  in- 
terlacing branches,  mossy  cells,  or  spider  cells. 
These  cells  develop  from  the  ectoderm  and  are  onto- 
genetically  closely  related  to  nerve  cells.  Their 
function  is  to  give  support,  not  to  conduct  nerve 
impulses. 

The  great  nerve  center  in  the  body  is  the  cerebro- 


Nucleus. 


Fig.  72.— Re- 
mak's  fibers 
(non  -  medullated 
fibers)  from  the 
pneumogastric 
nerve  of  a  rabbit 
(Bohm  and  Da- 
vidoff). 


TISSUES. 


105 


spinal  system — brain  and  spinal  cord.     Next  comes 
the  sympathetic  system,    made  up  of  ganglia  and 


Epineurium.    Perineurium. 


r:fe' :&:vwS^^^^Pl\  ^  Endoneuri 


Funiculus. 


Nerve  fibers  in 
cross  section. 


Artery  and  vein. 
Fig-  73- — Cross  section  of  nerve  trunk 


Neuraxis  of  peripheral 
sensory  neuron. 


Dendrite  • 

of  periph- 
eral sen- 
sory neu- 
ron. 

Nerve- 

trunk. 


Spinal  ganglion.  — -J-^ 


Anterior  horn  of  gray  matter 

of  spinal  cord. 

'  Neuraxis  of  peripheral  motor 
neuron. 

—  Sympathetic  ganglion. 

Neuraxis  of  sympathetic  neuron. 

Fig.  74. —  Diagram   to  show   the   composition   of  a   peripheral  nerve- 
trunk  (Huber). 

mostly  non-medullated  nerve  fibers  that  terminate 
in  glands  or  smooth  muscle.     Lastly,  the  peripheral 


106     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

system, — nerve  terminations  formed  in  tissues  and 
organs  throughout  the  whole  body. 

General  Considerations. — Nerve  cells  are  so  highly 
specialized  that  their  multiplication  after  birth  is  un- 
known. We  never,  therefore,  find  tumors  of  nerve 
cells.  If  a  nerve  cell  is  cut,  the  axis  cylinder  re- 
moved from  the  nerve  cell  dies  while  the  end  that 
is  still  attached  to  the  cell  regenerates  and  may 


Fig-  75« — Neurogliar  cells:   ay  from  spinal  cord  of  embryo  cat; 'ft,  from 
brain  of  adult  cat;   stained  in  chrome-silver  (Bohm  and  Davidoff). 

restore  the  lost  part.  Surgeons  unite  the  ends  of  a 
cut  nerve  so  that  the  axis  cylinder  may  develop  along 
the  old  nerve  trunk  which  becomes  a  path  of  least 
resistance. 

In  amputations  the  cut  nerve  may  grow  into  a 
tumor,  called  a  neuroma.  Such  a  tumor  would  con- 
sist of  nerve  fibers  and  the  accompanying  connective- 
tissue  elements.  Injury  to  nerve  cells,  such  as 


TISSUES.  107 

brain  or  ganglia,  heal  by  production  of  connective 
tissue  and  accompanying  scar. 

The  function  of  the  axis  cylinder  is  to  conduct 
a  nerve  impulse.  Physiologically  such  an  impulse 
travels  away  from  the  cell,  but  experimentally  it  may 
pass  in  the  opposite  direction,  as  is  the  case  when  a 
nerve  is  stimulated  midway  in  its  course.  The  axis 
cylinder  being  made  up  of  fibrils,  it  follows  that  such 
a  cylinder  may  conduct  more  than  one  impulse, 
which  in  turn  reach  different  centers  through  dif- 
ferent collaterals. 

The  function  of  the  medullary  sheath  is  to  protect 
and  nourish  the  axis  cylinder.  Experimentally  the 
non-medullated  nerve  fibers  will  tire  quicker  than 
the  medullated.  The  nodes  of  Ranvier  are  points 
where  nourishment  from  the  blood  and  lymph  can 
reach  the  cylinder.  It  is  affirmed  by  some  that  the 
endolemma  is  only  a  lymph  space  surrounding  the 
axis  cylinder. 

The  neurilemma  is  protective  in  function  and  gives 
great  strength  to  the  fibers.  With  nerves  that  ter- 
minate in  muscle  fibers  the  neurilemma  is  continuous 
with  the  sarcolemma  of  the  muscle.  Proximally  the 
neurilemma  begins  where  the  medullary  sheath  takes 
up,  always  a  short  distance  from  the  nerve  cell,  which 
leaves  the  axis  cylinder  uncovered  as  it  emerges  from 
the  cell. 

It  is  affirmed  that  the  neuron  represents  the  ele- 
mentary unit  of  nerve  tissue,  and  that  neurons  are 
merely  in  contact  with  each  other  and  not  in  proto- 
plasmic continuity.  This  idea  constitutes  the  neuron 
theory. 


CHAPTER  III. 

CIRCULATORY  SYSTEM,  BLOOD,  MARROW,  AND 
LYMPHATIC  ORGANS. 

HEART. 

The  heart  is  a  muscular  organ.  Its  wall  consists 
of  three  layers,  endocardium,  myocardium,  and 
epicardium. 

1.  The  endocardium  is  a  serous  membrane  that 
covers  the  inner  surface.     Histologically  it  consists 
of  two  layers,  an  inner  lining  of  simple  squamous 
epithelial  cells  (endothelium  or  mesothelium),  and 
an  outer  layer  composed  of  connective-tissue  fibers, 
connective-tissue  cells,   and  smooth  muscle  cells. 
The  endocardium  is  reflected  over  the  heart  valves 
where  the  smooth  muscle  is  particularly  abundant. 

2.  The  myocardium  is  the  middle  layer  and  forms 
the  mass  of  the  heart  wall.     It  consists  of  muscle 
tissue,  the  cardiac  muscle  already  described  (page  87) . 
This  muscle  consists  of  many  layers  that  course  in 
different  directions  with  connective-tissue  elements 
intervening,    in   which   branches   of   the   coronary 
blood-vessels  ramify. 

3.  The  epicardium  is  the  outer  covering,  a  serous 
membrane,  and  histologically  similar  to  the  endo- 
cardium, with  a  greater  deposit  of  fat.     The  epi- 
cardium is  reflected  to  form  the  pericardium,  the 

108 


CIRCULATORY   SYSTEM. 


109 


epithelial  cells  secreting  a  serous  fluid  that  acts  as  a 
lubricant. 

ARTERIES  AND  VEINS. 

Arteries. — The  arteries  convey  blood  from  the 
heart  to  the  capillaries,  and  vary  in  size  from  the 
aorta,  the  largest,  down  to  minute  structures  of  mi- 
croscopic caliber.  The  walls  of  these  vessels  are 
composed  of  three  layers :  tunica  intima,  media,  and 
adventitia. 

i .  Tunica  intima  is  the  internal  coat  and  is  a  very 


Fig.  76. — Cross  section  of  small  artery  and  vein;   A,  artery;  Vt  vein. 


thin,  smooth,  glassy  membrane,  often  difficult  to 
demonstrate  in  sections.  This  is  again  divided 
into  three  layers,  the  innermost  being  a  layer  of 
pavement  endothelial  cells,  outside  of  which  we  find 
a  delicate  fibrous  connective-tissue  fabric,  the  sub- 
endothelium,  and  outside  of  this  again  a  layer  of  elas- 
tic fibers  called  the  fenestrated  membrane  of  Henle. 
The  endothelial  layer  is  made  up  of  a  single  layer  of 
flattened  cells,  held  together  by  a  cement  substance 
and  analogous  to  the  endothelium  of  the  peritoneum 


110      NORMAL   HISTOLOGY  AND  .ORGANOGRAPHY. 

and  pleura  already  described.  These  cells  are  plas- 
tic, loosely  attached  to  the  subendothelium,  and 
form  a  slippery  surface  over  which  the  arterial 
blood  flows  rapidly.  Any  damage  to  these  cells 
results  quickly  in  the  formation  of  a  small  blood- 
clot  at  the  point  of  injury,  from  which  we  infer  that 
they  play  a  most  important  physiological  role  in 
their  relation  to  the  blood  stream.  The  subendo- 
thelium is  made  up  of  a  delicate  network  of  elastic 
fibers,  enclosing  a  few  connective-tissue  cells,  which 
allows  the  applied  endothelium  a  limited  amount  of 
mobility.  The  fenestrated  membrane  of  Henle  (called 
the  internal  limited  membrane  of  the  media  by 
some  authors)  consists  of  a  coarser  elastic  network 
of  heavier  elastic  fibers  which  when  peeled  away  as 
a  whole  presents  on  the  exposed  surface  a  basket- 
work  arrangement  of  its  fibers  with  numerous  in- 
tervening elongated  apertures  like  so  many  windows  > 
hence  its  name.  This  membrane  in  cross-section  of 
arteries  appears  as  a  wavy  or  corrugated  white 
line  encircling  the  artery  very  near  to  its  inner 
surface. 

2.  Tunica  Media. — This  is  the  middle  layer  of 
an  artery,  and  makes  up  the  bulk  of  its  wall.  In 
small  arteries  a  considerable  amount  of  smooth  cir- 
cular muscle  fibers  is  always  present,  while  in  the 
larger  arteries  circular  elastic  and  non-elastic  con- 
nective-tissue fibers  make  up  its  bulk.  A  sprinkling 
of  connective-tissue  cells  may  be  seen,  also  a  limited 
amount  of  longitudinal  muscle  and  connective-tis- 
sue elements.  A  few  blood  capillaries  and  lymphatic 
spaces  are  present,  which  always  connect  with  a 


CIRCULATORY   SYSTEM. 


Ill 


coarser  vascular  system  of  the  outer  layer,  never 
directly  with  the  blood  within  the  artery  through 
the  intima.  Of  course,  nerve  endings  are  found, 
which  can  only  be  demonstrated  in  specially  pre- 
pared sections. 

3.   Tunica   Adventitia. — This   is  the  outer   layer, 

—  Endothelium. 
Subendothelium. 
Fenestrated     mem- 
brane of  Henle. 


Vasa  vasorum. 
•  Fig-  77- — Cross  section  of  aorta. 

and  is  made  up  of  a  loose  arrangement  of  tissues,  and, 
taken  as  a  whole,  is  less  definitely  defined  than  the 
media.  It  varies  in  thickness  according  to  the  lo- 
cation of  the  artery,  but,  as  a  rule,  it  is  not  so  wide 
as  the  media;  while  in  the  media  the  connective- 
tissue  fibers  are  arranged  in  sheets  which  interlace 
with  any  muscle  that  may  be  present,  in  the  adven- 
titia  the  fibers  form  diagonal  bundles,  mostly  of  the 


112      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

non-elastic  kind,  which  mingle  with  the  adjacent  are- 
olar  tissue  with  which  arteries  are  nearly  always  as- 
sociated. These  bundles  often  serve  as  support  to 
organs,  by  which  the  latter  are  more  firmly  an- 
chored. From  such  a  union  between  the  vena  cava 
and  abdominal  aorta  to  the  liver  this  organ  receives 
a  substantial  support.  The  kidneys  and  ovaries 
are  organs  that  may  be  cited  as  benefiting  greatly 
by  such  a  connection.  A  considerable  amount  of 
fat  is  often  present  in  the  adventitia,  also  connective- 
tissue  cells,  nerves,  a  few  smooth  muscle  fibers, 
lymphatics,  and  blood-vessels.  The  latter  are 
called  vasa  vasorum,  and  play  an  important  part  in 
the  nourishment  of  the  arterial  wall.  The  vasa 
vasorum  are  sub-branches  derived  usually  from 
some  small  branch  of  an  adjacent  artery,  but  may 
come  directly  from  a  small  branch  of  the  same  artery 
which  is  given  off  at  a  higher  point. 

As  stated  before,  large  arteries  have  relatively  a 
large  amount  of  elastic  fibers  and  a  small  amount  of 
smooth  muscle.  The  aorta  has  scarcely  any  muscle. 
In  the  small  arteries  the  reverse  is  true.  The  wall 
of  large  arteries  is  relatively  thinner  than  that  of 
small  ones.  The  reverse  is  true  of  the  intima.  In 
large  arteries  the  adventitia  is  also  relatively  scant, 
while  in  the  smaller  ones  the  adventitia  may  be  one- 
half  to  two-thirds  the  thickness  of  the  media.  On 
account  of  the  rigid  and  elastic  arterial  wall  these 
vessels  are  usually  empty  after  death,  contracted 
but  retain  their  normal  shape;  while  veins,  on  the 
other  hand,  collapse  and  usually  contain  a  certain 
amount  of  blood. 


CIRCULATORY  SYSTEM.  113 

Veins. — These  vessels  convey  the  blood  from  the 
capillaries  back  to  the  heart.  The  progressive  in- 
crease in  size  and  the  thickness  of  their  walls  is 
accompanied  by  a  relative  increase  in  blood  pressure 
and  rate  of  blood  flow,  yet  nowhere  is  this  equal  to 
what  obtains  in  the  large  arteries.  Structurally 
we  find  the  same  layers  in  veins  as  in  arteries,  with 
the  chief  difference  that  the  vein  wall  is  much  thinner. 
The  endothelial  layer  of  cells  is  supported  by  a 
very  thin  layer  of  delicate  connective-tissue  fibers, 
mostly  non-elastic,  while  the  fenestrated  mem- 
brane of  Henle  is  incomplete  and  usually  difficult 
to  demonstrate.  The  media,  as  in  arteries,  is  the 
most  prominent  layer,  but,  unlike  arteries,  the  non- 
elastic  fibers  prevail.  Smooth  muscle  fibers,  mostly 
circular,  are  often  significant  in  this  layer,  while 
the  other  tissue  elements  are  less  conspicuous. 
The  adventitia  resembles  more  closely  that  found 
in  arteries,  with  perhaps  even  less  of  the  elastic  ele- 
ments and  more  of  the  smooth  muscle  cells.  Com- 
paring the  different  sizes  of  veins,  we  find  an  excess 
of  elastic  and  muscular  tissue  in  large  veins.  In 
the  pulmonary  vein  the  circular  muscle  fibers  are 
well  developed,  while  in  the  large  cranial  veins, 
such  as  the  meningeal  sinuses,  muscle  tissue  is  almost 
entirely  absent.  Veins,  like  arteries,  therefore, 
show  a  structural  variation,  depending  not  only  on 
size,  but  on  location.  It  should  be  mentioned  that 
in  many  superficial  long  veins,  like  those  of  the  legs 
and  neck,  valves  are  present  in  the  form  of  crescentic 
folds  of  the  intima  which  function  in  overcoming 
the  pressure  of  blood  due  to  gravity.  Those  of  the 


IT 4      NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 

neck  are  so  placed  as  to  become  functional  when  an 
animal  lowers  its  head,  as  in  the  act  of  grazing. 

SUMMARY  OF  ARTERIES  AND  VEINS. 

I.     Tunica  intima. 

1.  Endothelium,  simple  squamous  epithelial  cells. 

2.  Subendothelial  layer. 

*(a)  White  connective- tissue  fibers. 
(b)  Connective- tissue  cells. 
f(c)  Elastic  connective-tissue  fibers. 

ts.  Henle's  fenestrated  membrane  (elastic  internal  limiting  mem- 
brane).   Interlacing  basketwork  of  elastic  fibers. 
II.     Tunica  media. 

fi.  Smooth  muscle,  circular. 

f2.  Elastic  plates  and  fibers,  longitudinal  and  circular. 

3.  Nerves. 

4.  Blood  capillaries,  difficult  to  demonstrate. 
*5.  White  connective  fibers. 

6.  Connective-tissue  cells. 

7.  Muscle  fibers  longitudinal,  rare. 
III.     Tunica  adventitia. 

*i.  White  connective- tissue  fibers,  longitudinal  and  oblique. 

2.  Connective- tissue  cells. 

ts-  Elastic  connective-tissue  fibers,  longitudinal  (external  limit- 
ing membrane). 

4.  Nerves. 

5.  Vasa  vasorum  (blood-vessels). 

6.  Lymphatic  vessels  and  nodes. 
*7.  Smooth  muscle  fibers. 

It  should  be  remembered  that  structural  difference 
in  large  and  small  arteries  is  in  keeping  with  their 
function.  In  small  arteries  or  arterioles,  the  involun- 
tary muscle  is  conspicuous,  as  it  is  the  contraction  of 
this  muscle  that  regulates  the  blood  supply  to  an 
organ.  In  large  arteries,  as  the  aorta,  the  muscle  is 

*  This  tissue  predominates  in  veins, 
f  This  tissue  predominates  in  arteries. 


CIRCULATORY   SYSTEM. 


•  Endothelium. 

'"  "_-  •  .-"".;•: Subendothelium. 

Fenestratedmem- 
brane  of  Henle, 
'  Media. 


Fig. 


, 

78. —  Cross   section    of   small 
artery. 


unnecessary  and  is  greatly  reduced,  while  elastic  ele- 
ments are  unusually  well  developed.   The  muscle,  too, 
is  deficient  in  large  veins  situated  deep  in  the  body, 
as  the  vena  cava.    Many 
of  the  smaller  and  more 
superficial     veins      have 
valves,   folds    of  the  in- 
tima,  so  arranged  as  to 
equalize  the  gravity  press- 
ure    of     the     contained 
blood.       Without     these 
valves     the     thin-walled 
veins       would      become 

greatly  distended.  If  for  any  cause  the  veins  ex- 
pand so  that  the  valves  do  not  act,  a  permanent 
distention  with  engorgement  of  blood  follows.  The 
veins  become  distorted  and  are  spoken  of  as  varicose 

veins,  a  condition  quite 
common  to  the  long 
saphenous  veins  of  the 
lower  limbs. 

Capillaries.  — These 
are  the  finer  organic 
ramifications  of  the 
circulatory  system,  and 
unite  arteries  and 
veins.  Histologically, 
the  walls  of  capillaries 


Intima. 


Media. 


Adventilia. 


Vasa  vasorum. 

Fig.  79. —  Cross  section  of  vein. 


consist  of  a  single  layer 
of  flattened  epithelial  (endothelial  or  mesothelial) 
cells.  The  blood  courses  very  slowly  through  these  in- 
terlacing tubes.  The  white  cells  penetrate  the  walls 
and  under  certain  conditions  even  the  red  corpuscles 


Il6      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

may  do  so.  According  to  some  investigators,  minute 
pores  in  the  epithelial  wall,  called  stigmata  and  sto- 
mata,  allow  this  migration.  Others  deny  the  presence 
of  these  spores,  in  which  case  the  blood  elements 
escape  by  passing  between  two  adjacent  epithelial 
cells,  after  which  this  opening  closes. 


Flat  view. 


Side  view. 


THE  BLOOD. 

The  blood  is  derived  from  the  mesoderm;  it  is  a 
red  fluid  that  consists  of  (i)  a  liquid  portion,  the 
plasma,  and  (2)  solid  constituents,  the  corpuscles. 
There  are  at  least  three  classes 
of  the  latter,  red  corpuscles,  white 
corpuscles,  and  platelets. 

i.  Red  corpuscles  (erythro- 
cytes)  in  the  mammalia  are  non- 
nucleated,  circular,  biconcave 
discs.  In  all  the  other  verte- 
brate groups  and  in  all  embryos 
they  are  nucleated  oval  and 
biconvex  cells.  Each  corpuscle 
consists  of  a  red  coloring  matter, 
hemoglobin,  and  a  more  substan- 
tial fabric  or  reticulum,  the 
stroma.  The  hemaglobin  is  the 
bearer  of  oxygen,  is  readily  solu- 
ble in  water,  leaving  the  stroma 
or  fabric,  which  is  then  known  as 
a  ghost  corpuscle. 

The  red  corpuscles  are  soft  and 
elastic  and  are  covered  by  an  oily 
film.  In  a  fresh  spread  they  adhere  to  each  other 
by  their  concave  surfaces  forming  rouleaux  or  "  money  - 


Rouleau. 


Rouleau. 


Fig.     80.— Red     blood- 
corpuscles  from  man. 


CIRCULATORY  SYSTEM. 


117 


pile"  rows.  This  is  purely  a  physical  phenomenon.  As 
soon  as  the  oily  covering  dissolves  this  combination 
disappears.  The  corpuscles  are  extremely  susceptible 
to  changes  in  the  plasma.  If  water  is  added  they  will 
swell  up  and  the  hemoglobin  begins  to  dissolve.  With 
evaporation  the  corpuscles  begin  to  shrink,  forming 
minute  processes  and  they  are  then  said  to  be 
crenated.  Evaporation  of  water  produces  an  in- 
creased percentage  of  the  salts 
in  solution.  This  in  turn  ab- 
stracts water  from  the  cor- 
puscles and  the  shrinking  or 
crenated  condition  follows. 

It  is  estimated  that  the  total 
amount   of  blood   in  man  is 

one-thirteenth  the  weight  of  the  body.  The  average 
normal  male,  therefore,  has  approximately  25,000,- 
000,000,000  red  corpuscles.  The  life  period  of  a  red 


Fig.    81. —  Crenated    red 
blood-corpuscles  from  man. 


Fig.  82.— Red  blood-corpuscle  of  frog;    a,  flat  view;    6,  side  view. 

corpuscle  is  not  definitely  known,  but  physiologists 
tell  us  it  is  probably  from  two  to  four  weeks.     Ac- 


Il8      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


cordingly  the  daily  consumption  and  loss  is  enormous, 
and  is  equaled  only  by  as  constant  and  regular  a 
production  of  new  cells.  Their  number  in  man  is 
5,000,000  per  cubic  millimeter. 

The  following  table  gives  the  size  of  the  red  blood- 
corpuscle  in  the  different  groups  of  animals : 


Man    7.2  to  7.8  ft. 

Monkey 7.0  ft. 

Dog 7.5  ft. 

Cat 6.2  ft. 

Horse 5.6  ft. 


Chick.  ..  .12.1  by    7.2  p. 

Duck 12.9   "      8.0  ft. 

Tortoise.  .21.2    "    12.5  ft. 

Snake 22.0   "    13.0/1. 

Frog 22.3    "    15.7  ft. 


Guinea-pig  .  . 


7.5 


Newt  .  .  ..30.7 


19.0  ft. 


White  Corpuscles. — These  are  colorless,  nucleated, 
plastic,  ameboid  cells.  Their  number  in  man  is 
from  7000  to  10,000  per  cubic  millimeter.  They  are 
variously  classified  according  to  the  morphology  of 
their  nuclei,  or  the  granules  in  the  cytoplasm  that 


Small 

mononuclear. . 


Fig.  83. — White  blood-corpuscles  from  man. 


take  different  stains,  or  as  to  their  origin,  or  as  to 
their  function.  For  practical  purposes  they  may 
be  classified  as : 

1.  Lymphocytes size   8  to  10  microns.  ...  22  per  cent. 

2.  Large  mononuclear  leucocytes.   *'    iotoi5       "       ....4    "      " 

3.  Polynucleated "    12  "       ....74    "      " 

(a)  Mast  cells 0.4  per  cent. 

(b)  Eosinophiles 2  to  4    "      " 

(c)  Neutrophiles 70    u      " 


CIRCULATORY    SYSTEM.  Iig 

Lymphocytes  are  small,  mononucleated,  white  cor- 
puscles, with  a  distinct  staining  nucleus  and  a  very 
narrow  border  of  cytoplasm.  Amoeboid  motion  is, 
accordingly,  much  limited  in  this  class. 

Large  mononucleated  leucocytes  have  a  large  vesic- 
ular and  usually  eccentric  nucleus.  Its  chromatin 
occurs  in  scattered  granules  that  stain  less  deeply 
with  nuclear  stains,  while  the  finely  granular  cyto- 
plasm is  usually  abundant.  These  cells  are  gener- 
ally regarded  as  phagocytic  in  function. 

Polynuclear  cells  are  only  slightly  larger  than  the 
red  blood-corpuscles.  The  nuclei  are  often  nodular, 
polymorphic;  that  is,  are  united  by  slender  constric- 
tions, or  are  lobulated  and  of  a  variety  of  patterns. 
In  a  small  number  of  these  cells  basophilic  granules 
are  found  in  the  cytoplasm,  which  stains  blue  with 
basic  stains.  These  are  the  mast  cells.  Another 
small  group  have  eosin-staining  granules,  and  these 
are  the  eosinophiles.  The  large  bulk  of  poly  nucleated 
white  corpuscles  have  cy  toplasmic  granules  that  take 
neither  acid  nor  basic  stains,  and  these  are  the  neu- 
trophiles.  They  are  the  white  corpuscles  found  abun- 
dantly in  ordinary  pus  and  the  ones  that  produce  a 
general  leucocytosis  in  such  infections. 

The  percentage  of  these  different  cells  and  their 
total  number  per  cubic  millimeter  is  of  the  greatest 
clinical  value  in  blood  analysis.  They  are  often 
called  wandering  cells,  as  they  are  able  to  pass 
through  the  capillary  wall  and  migrate  throughout 
the  tissues  and  organs.  The  poly  nucleated  form  is 
readily  recognized  by  multiple  or  fragmented  nuclei. 

3.  Blood  platelets  are  small,  colorless,  round,  non- 
nucleated  bodies  about  one-third  the  size  of  red 


120      NORMAL   HISTOLOGY   AND  ORGANOGRAPHY. 

blood-corpuscles.    They  are  supposed  to  play  an  im- 
portant role  in  the  coagulation  of  blood.     As  soon 


r 

Fig.  84. —  Ehrlich's  leucocytic  granules  (from  preparations  of 
H.  F.  Miiller):  a,  Acidophile  or  eosinophile  granules,  relatively  large 
and  regularly  distributed;  e,  neutrophile  granules;  /?,  amphophile 
granules,  few  in  number  and  irregularly  distributed;  ?,  mast  cells  with 
granules  of  various  sizes;  d,  basophile  granules;  (a,  o,  and  e,  from  the 
normal  blood;  ?-,  from  human  leukemic  blood;  /?,  from  the  blood  of 
guinea-pig)  (Bohm  and  Davidoff). 

as  blood  is  shed  most  of  them  disappear,  unless  spe- 
cial precaution  is  made  to  preserve  them.  They  may 
be  preserved  by  pricking  the  finger  through  a  drop 
of  osmic  acid.  Their  number  per  cubic  millimeter 
is  from  200,000  to  600,000. 

According  to  Wright's  investigations,  these  plate- 
lets represent  detached  portions  of  giant  cells  found 
in  bone-marrow  or  in  the  spleen.  Schafer  regards 
them  as  minute  cells,  while  others  think  of  them  as 
fragments  of  red  or  white  corpuscles. 

Hemin  Crystals  (Teichman's  crystals). — These 
come  from  the  hemoglobin  of  the  blood,  and  when 
found  are  always  a  positive  evidence  of  blood.  The 
crystals  can  be  obtained  from  clotted  blood,  no  mat- 


CIRCULATORY   SYSTEM. 


121 


ter  how  old  the  clot  or  stain  is.  Dry  blood  and  salt, 
equal  parts,  are  ground  together  on  a  glass  slide,  a 
few  drops  of  glacial  acetic  acid  are  added  and  heat 
applied  until  gas-bubbles  appear.  The  crystals  are 
brown,  rhombic,  and  easily  recognized. 


Fig.  85. — Crystallized  hemoglobin:  a,  6,  Crystals  from  venous  blood 
of  man;  c,  from  the  blood  of  a  cat;  d,  from  the  blood  of  a  guinea-pig; 
e,  from  the  blood  of  a  hamster;  /,  from  the  blood  of  a  squirrel  (after 
Frey). 

MARROW. 

Bone  marrow  is  either  white  or  red.  The  white 
marrow  occupies  the  shaft  of  the  bone  and  is  largely 
fat.  The  red  is  found  in  the  ends  of  bones  or  can- 
cellated portions  and  is  richly  supplied  with  blood. 


122      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

Histologically,  we  find  in  marrow  all  the  con- 
stituents of  blood  and  connective-tissue  elements, 
fibers  and  cells.  In  addition,  the  following  are  some 
of  the  more  characteristic  cells  of  this  tissue  : 

i  .  Hematoblasts  or  Nucleated  Red  Blood-corpuscles. 
—  These  cells  contain  hemaglobin  and  a  small  round 
nucleus  that  stains  heavily  with  hematoxylin.  They 
are  supposed  to  be  the  chief  source  of  the  red  blood- 
corpuscle,  in  which  case  the  nucleus  must  disappear 
either  by  disintegration  or  extrusion. 

2.  Marrow  Cells  or  Myelocytes.  —  These  are  large 
cells  with  a  rather  large  nucleus  that  stains  lightly. 

3.  Eosinophiles.  —  These  are  destined  to  become 
the  eosinophile  of  the  blood. 

4.  Giant    Cells    (myeloplaxes    or    osteoclasts)  .— 
These   are   very  large   poly  nucleated    cells,  having 
from  ten  to  twenty  nuclei.     Cells  of  this  class  are 
not  numerous,  but  extremely  large  (30  to  100  /w). 

They  may  be  found  in  the  fetal 
liver  or  spleen,  and  are  very  char- 
acteristic of  developing  bone.  They 
present  a  finely  granular  proto- 
plasm without  any  cell  wall.  The 
™clei  are  bunched  about 


tais  from  blood-     the  center  of  the  cell,  and  in  this 

stains  of  man.  -  -._.       f  - 

respect  they  differ  from  the  giant 
cells  found  in  tuberculosis  foci,  in  which  the  nuclei 
are  found  near  the  periphery.  They  multiply  by 
mitosis,  and  primarily  are  supposed  to  be  derived 
from  leucocytes  by  endogenous  division  of  their 
nuclei.  These  remarkable  cells  have  usually  been  re- 
garded as  the  active  agents  in  bone  absorption,  but 
recently  Wright  has  suggested  that  blood  platelets 


CIRCULATORY   SYSTEM. 


123 


may  be  derived  from  their  cytoplasm  by  a  process 
of  budding  or  by  particles  merely  breaking  away. 

General  Considerations. — There  is  an  old  saying 
that  "a  person  is  as  old  as  his  blood."  A  truer  ex- 
pression would  be  that  he  is  as  old  as  his  blood- 
vessels. With  age,  or  dissipation,  the  blood-vessels 
harden,  due  to  depositions  of  connective-tissue  ele- 
ments. This  impairs  the  free  circulation  of  blood  and 
the  body,  as  a  whole,  suffers. 
The  hardened  condition  is  /':V^?>... 

spoken  of  as  arteriosclerosis, 
or  atheroma.  Usually  the  in- 
tima  suffers  first  by  becoming 
much  thickened.  Later,  a 
like  disturbance  takes  place 
in  the  media  and  adventitia. 
As  superficial  scars  remain 
permanently,  and  can  not  be 
eliminated,  so  there  is  no  re- 
lief for  this  scar  formation  of 
the  blood-vessels.  Under  this 
hardened  condition  a  rupture 
of  the  smaller  arteries  is  not 
uncommon,  particularly  those 
of  the  brain,  as  they  have 
thinner  walls.  Such  a  disas- 
ter is  apt  to  be  fatal. 

An    inflammation    of    the 

heart,  as  endocarditis,  is  apt  to  produce  a  deposit  of 
connective  tissue  in  the  endocardium,  which  upon 
shrinking  brings  about  defective  valves,  with  leak- 
age of  blood.  This  increases  the  work  of  the  heart, 
and  although  that  organ  in  an  emergency  can  do 


Hematoblasts. 


Eosinophile. 


Marrow  cell. 


Giant  cell. 


Fig.  87. — Cellular  elements  of 
red  marrow. 


124      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


twenty  times  its  normal  work,  there  is  of  course  a 
limit  to  its  power,  and  broken  compensation  sooner 
or  later  follows. 

The  vasa  vasorum,  that  carry  blood  to  nourish  the 
walls  of  both  arteries  and  veins,  are  very  important 
structures.  The  coronary  vessels  of  the  heart  be- 
long to  this  class  and  their  course  is  quite  definitely 
known.  Our  knowledge  of  the  rest  is  vague.  They 
ramify  through  the  adventitia  and  to  a  less  extent 

in  the  media.    If  a 

xft^vffi|$.f|X.  ..  Giant  cell. 


£$ip 


'  Hematoblast. 


Fat  space. 


blood  -  clot  forms 
within  the  vessel, 
loops  from  thejvasa 
vasorum  enter  the 
clot  and  assist  in 
its  organization. 

The  endothelial 
cells  of  the  intima, 
according  to  one 
theory,  are  active 
agents  in  preserv- 
ing the  fluid  con- 
dition of  the  blood ; 
that  is,  inhibiting 
coagulation.  If  these  cells  are  injured  a  clot  of 
blood  quickly  forms  upon  the  injured  or  denuded 
surface.  Surgeons  take  advantage  of  this  principle 
and  twist  or  crush  the  ends  of  bleeding  vessels  to 
check  a  hemorrhage. 

The  disintegration  of  red  blood-corpuscles  is  known 
as  hemolysis,  and  may  be  produced  by  injecting  into 
the  circulatory  system  certain  poisons,  or  mixing 
extravasated  blood  directly  with  these  poisons. 


Fig.  88. — Section  of  red  marrow. 


CIRCULATORY   SYSTEM. 


125 


Hemolysis  occurs  in  various  diseases  and  is  one  of 
the  chief  changes  observed  in  making  a  Wasser- 
mann  test. 

The  identification  of  blood-stains  is  often  a  medico- 
legal  problem.  The  corpuscles  of  the  blood  pre- 
serve their  integrity  for  a  remarkably  long  period  of 
time,  so  that  in  a  water  solution  of  even  an  old  clot, 


Capsule. 
Trabeculce. 
Germinal  center. 
Lymph  sinus 


- 


<i' ^V&yfiXf&.-.J^eXfS'j'  v^  ^L. ^=^-ef 


Fig.  89. — Section  of  lymph  node. 

the  red  blood-corpuscles  are  readily  detected  under 
the  microscope.  Hemin  crystals  is  another  evidence 
that  the  stain  is  blood.  To  identify  the  blood  of 
man  is  practically  impossible.  Non-mammalian 
blood,  as  that  of  a  bird,  can  usually  be  positively 
recognized  by  the  nucleated  red  blood-corpuscles 
and  their  oval  form.  The  practical  value  of  this  in 
criminal  cases  is  apparent. 

LYMPHATIC  SYSTEM,  THYMUS,  AND  SPLEEN. 

i.  Lymphatic  Capillaries. — The  walls  of  these 
capillaries  consist  of  a  single  layer  of  flattened 
epithelial  cells  (mesothelial  or  endothelial).  They 


126      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

therefore,  histologically,  resemble  the  blood-capil- 
laries. They  are  not  so  well  defined  but  represent 
rather  irregular  cavities  with  numerous  constrictions. 
These  capillaries,  according  to  one  theory,  form  a 
closed  system  and  open  only  into  the  larger  vessels. 


• 

Muos is.  ^ 


Fig.  90. —  From    a  human    lymph  gland.     At  a  are  seen  the   con- 
centrically arranged  cells  of  the   lymph   nodules  (fixation   with    Flem 
ming's  fluid)  (Bohm  and  Davidoff). 

Another  theory  is  that  at  their  origin  they  communi- 
cate with  intercellular  spaces. 

2.  Lymphatic  Vessels. — These  accompany  blood- 
vessels and  have  very  thin  walls.  Ultimately  they 
drain  into  the  large  thoracic  lymph  duct  or  the  short 
right  lymphatic  duct;  each  finally  opens  into  the 
venous  system  at  the  junction  of  the  subclavian  and 
jugular  veins.  The  thoracic  duct  begins  with  the 
receptaculum  chili,  just  below  the  diaphragm  and  a 
little  to  the  right  of  the  vertebrae,  passes  upward  into 
the  thorax  to  open  into  the  venous  system  on  the 


CIRCULATORY   SYSTEM. 


127 


left  side,  as  given  above.    The  histology  of  the  walls 
of  these  vessels  resembles  that  of  the  veins. 

3.  Lymph  Glands.. — These  represent  adenoid  tis- 
sue, and  consist  of  (i)  reticular  connective  tissue  and 
(2)  lymph  cells.  Lymph  glands  are  found  throughout 
the  body  in  connection  with  lymph  vessels,  fat  and 
connective  tissue.  They  serve  as  filters  to  the  lymph 


Gland. 


Fig.  91. —  A  solitary  lymph  nodule  from  the  human  colon.  At 
a  is  seen  the  pronounced  concentric  arrangement  of  the  lymph  cells 
(Bohm  and  Davidoff). 

and  contribute  white  corpuscles  to  the  blood. 
Structurally,  these  nodes  have  a  connective-tissue 
capsule,  that  sends  filaments  into  the  node,  called 
trabecula.  Within  these  meshes  lymph  cells  are 
densely  packed  around  the  periphery  of  secondary 
nodules,  which  in  turn  occupy  the  cortex  of  each 
node.  The  center  of  each  nodule  is  known  as  the 
germ  center  or  lymph  pulp.  The  periphery  of  each 
secondary  nodule,  being  densely  packed  with  white 
lymph-corpuscles,  takes  a  darker  stain  than  the 


128     NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

center.  The  space  occupied  by  these  white  corpus- 
cles is  called  the  lymph  sinus.  The  cells  of  the  sinus 
are  in  circulation  while  those  of  the  germ  center 
remain  stationary. 

Lymph  glands  represent  adenoid  tissue  and  con- 
sist of  two  elements,  (a)  reticular  connective  tissue, 
with  many  elastic  fibers,  and  (fc)  lymphoid  cells.  An 
inflammation  of  this  tissue  is  therefore  called  adeni- 
tis. Blood-vessels  and  nerves  ramify  through  this 
tissue.  They  enter  at  one  point  called  the  hilum. 
Lymph  vessels  connect  with  opposite  points  of  the 
node,  the  efferent  one  passing  out  at  the  hilum.  The 


Fig.  92. —  A  small  lobule  from  the  thymus  of  child,  with  well- 
developed  cortex,  presenting  a  structure  similar  to  that  of  the  cortex 
of  a  lymph  gland  (Bohm  and  Davidoff). 

efferent  quickly  unites  with  a  second  node  to  which  it 
becomes  the  afferent  vessel.  In  this  way  the  lymph 
nodes  are  united  into  chains,  always  accompanying 
blood-vessels  and  fascia. 

Solitary  lymph  nodes  are  found  just  beneath  the 
epithelium  of  mucous  membranes,  particularly  in 
the  alimentary  tract.  They  resemble  secondary 
nodules  of  lymph  nodes.  In  the  lower  part  of  the 


CIRCULATORY   SYSTEM. 


129 


ileum  they  are  collected  into  patches  called  agmi- 
nated  lymph  nodules  or  Peyer's  patches. 

Hemolymph  Glands. — These  resemble  the  lymph 
nodes  described  above,  except  that  the  lymph  sinus 
is  filled  with  blood.  When  first  discovered  they  were 
believed  to  be  evidence  of  disease,  but  they  are  now 
looked  upon  as  normal  structures.  They  are  most 
readily  found  in  the  fascia  involving  the  thoracic 
aorta,  and  are  particularly  abundant  in  the  sheep. 


Fig.  93. —  Section  of  lobule  of  thymus  gland. 

THYMUS  GLAND. 

The  thymus  gland  is  described  in  this  place  be- 
cause of  its  resemblance  in  the  adult  to  a  lymph 
organ.  In  the  embryo  it  is  an  epithelial  organ  that 
develops  from  the  hypoderm  of  the  third  and  fourth 
visceral  clefts.  Lymphoid  tissue  invades  this  epithe- 
lium and  reaches  its  highest  development  in  a  child 
two  years  old.  After  this  age  the  lymphoid  tissue  is 
9 


130      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

invaded  by  connective  tissue  and  fat,  so  that  at  the 
age  of  puberty  only  a  remnant  of  the  original  struc- 
ture remains. 

In  the  child  the  thymus  is  a  paired,  elongated, 
lobulated,  ductless  organ  that  lies  partly  in  the  neck 
and  partly  in  the  thorax  upon  the  large  blood- 
vessels. Structurally  we  recognize  a  capsule  with 
trabeculcz,  pulp  and  the  corpuscles  of  Hassal. 

1.  Capsule  and  Trabeculcz. — The  capsule  consists 
of  dense  connective  tissue,  mostly  nonelastic  fibers 
and  cells.     Processes  or  trabeculcz  pass  into  the  or- 
gan from  the  capsule  and  divide  it  up  into  distinct 
angular  lobules.     Fibers  from  the  trabeculae  enter 
the  lobules  where  they  interlace  to  form  a  supporting 
reticulum. 

2.  Pulp. — This  consists  of  lymphoid  cells  that  fill 
the  intersticies  of  each  lobule.     The  cells  are  more 
densely  packed  along  the  periphery  of  each  lobule, 
so    that   an   outer   or  cortical  layer  can  be  distin- 
guished from  a  central  portion,  the  medulla. 

3.  Corpuscles  of  Hassal. — 
These  are  nests  of  epithelial 
cells  that  lie  in  the  medulla 
and  are  remnants  that  show 
the  epithelial  origin  of  the  or- 

Fig.    94. — Corpuscle    of  ^*  ,     .  .,        ..1 

Hassal  surrounded  by  lym-     gan.     They  stain  red  with  eo- 

.  J       •> 


phoid  cells  from    the   me-      sin  an(J  are  found  in  no  other 

dulla. 

organ.      It    is    affirmed    that 

these  epithelial  cells  continue  to  grow  after  birth  and 
may  be  found  late  in  life  when  only  remnants  of  the 
thymus  is  present. 


CIRCULATORY   SYSTEM. 


SPLEEN. 

The  spleen  is  a  blood-forming  organ,  very  vas- 
cular, purple  in  color,  and  with  a  density  slightly 
more  than  that  of  the  liver.  It  varies  greatly  in 
size,  the  average  being  five  inches  long  and  three 
inches  wide.  Its  surfaces  touch  the  left  kidney,  the 
cardiac  end  of  the  stomach,  and  the  left  lower  aspect 
of  the  diaphragm.  Its  long  axis  follows  the  direction 
of  the  tenth  rib.  It  is  practically  covered  by  the 


Vein. 


Malpighian 
corpuscle. 


Trabecula. 


Artery. 
Spleen  pulp. 


pig.  9^ — Portion  of  section   of  human   spleen.     The   figure   gives   a 
general  view  of  the  structure  of  the  spleen  (Sobotta). 

peritoneum.  The  structures  to  be  recognized  are 
capsule  and  trabecula,  Malpighian  corpuscles,  and 
spleen  pulp. 

i.  Capsule  and  Trabeculcz.—^he  investing   peri- 
toneum forms  a  serous  coat  with  simple  squamous 


I32      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

epithelium  and  connective-tissue  fibers.  Subjacent 
to  this  the  spleen  is  provided  with  a  strong  cap- 
sule consisting  of  elastic  fibers,  connective-tissue 
cells  and  involuntary  muscle.  The  spleen  is  thus 
not  only  distensible  but  may  pulsate.  From  the 
deep  surface  of  the  capsule  processes  or  trabeculce  of 
connective  tissue  and  smooth  muscle  pass  into  the 
substance  of  the  spleen.  From  the  trabeculae  finer 
branches  pass  to  form  a  fine  supporting  fabric  for 
the  whole  organ. 


Fig.  96. —  Section  of  spleen. 

2 .  Malpighian  Corpuscles. — These  are  lymph  pock- 
ets in  the  adventitia  of  the  smaller  arteries.     The 
artery  rarely  passes  through  the  center  of  the  cor- 
puscle, but  usually  eccentric  to  or  one  side  of  it.    The 
lymph  corpuscle  is  liberally  supplied  with  blood. 

3.  Spleen  Pulp. — This  constitutes  the  bulk  of  the 
spleen  and  fills  the  spaces  between  the  trabeculae. 
The  constituent  corpuscles  of  the  blood  are  present 
in  this  pulp  and  splenic  cells.     The  latter  are  slightly 


CIRCULATORY   SYSTEM. 


133 


larger  than  white  blood-corpuscles,  are  mononu- 
cleated  and  contain  pigment  and  frequently  red 
blood-corpuscles . 

Blood  Supply. — The  splenic  artery  enters  the  hilum 
and  its  branches  follow  the  trabeculae.  Ultimately 
the  smaller  branches  enter  the  spleen  pulp.  Beyond 
the  Malpighian  bodies  the  smaller  arteries  end  in 
minute  dilatations  known  as  the  ampulla  of  Thoma. 
Beyond  these  the  blood  flows  directly  into  the  meshes 


Larger  fibers  of 
a  Malpighian 
body. 

Reticular  fibril 
(G  it  ter  las- 
em). 


Fig.  97. —  From  the  human  spleen  (chrome-silver  method)  (Bohm  and 

Davidoff). 

of  the  spleen  pulp  with  no  other  walls  than  the  spleen 
cells.  The  veins  begin  in  the  same  way  as  the 
arteries  end.  The  capillary  veins  pass  directly  to 
the  trabeculae  and  ultimately  unite  at  the  hilus  to 
form  the  splenic  vein  which  drains  into  the  portal. 

General  Considerations.— The  invasion  of  bacteria 
into  the  system  is  chiefly  along  the  lymphatics. 
Each  lymph  node  becomes  a  point  of  resistance,  and 


134    NORMAL  HISTOLOGY  AND   ORGANOTHERAPY. 

usually  enlarges  many  times  the  normal  size,  far  in 
advance  of  the  seat  of  infection.  This  is  due  to  the 
absorption  of  the  toxins.  Thus  the  lymph  nodes  in 
the  groin  enlarge  from  an  infection  in  the  toe,  those 
in  the  axilla  from  an  infected  finger,  and  those  of  the 
neck  from  a  bad  tooth.  If  these  barriers  break  down 
the  infection  becomes  systemic,  a  condition  known  in 
a  general  way  as  blood-poisoning. 


Artery  to  one  of 
the  ten  com- 
partments. 

Intralobular  \ 
artery. 

\ 

Interlobular 
trabecula.    \ 


•  l 


Intralobular  L_ 
trabecula.    \ 

|  \ 

Malpighian 
corpuscle.    [  m  | 


Intralobular 

venous  spaces. 
Intralobulor 
vein. 

Ampulla,  of 
Thoma. 

Spleen  pulp  cord. 
Interlobular  -vein. 
1  ntrfilobular  vein. 


Fig.  98. —  Diagram  of  lobule  of  the  spleen  (Mall). 

The  function  of  the  thymus  gland  is  not  known. 
Since  its  structure  resembles  the  tissue  of  a  lymph 
node  it  is  reasonable  to  suppose  that  it  has  a  like 
function.  Recently  structural  changes  have  been 
observed  in  this  organ  in  epileptics,  but  whether 
these  changes  are  a  cause  or  a  consequence  of  the  dis- 
ease is  not  known. 

The   lymphoid   tissue    of   the    spleen    no    doubt 


CIRCULATORY    SYSTEM.  135 

contributes  to  the  supply  of  white  blood-corpuscles. 
The  broken-down  red  corpuscles  found  in  this  organ 
have  led  to  the  further  idea  that  the  spleen  is  a 
graveyard  for  the  worn-out  red  corpuscles  of  the 
blood.  Leucocytes  are  supposed  to  feed  upon  this 
detritus  and  then  migrate  to  the  liver,  where  it  is 
elaborated  into  the  bile  pigment  of  that  organ. 

Anything  that  causes  an  enlargement  of  the  lymph 
nodes  usually  causes  an  enlargement  of  the  spleen. 
Like  these  nodes  the  spleen  is  capable  of  enormous 
distention,  due  to  the  abundance  of  elastic  con- 
nective-tissue fibers.  This  is  particularly  so  in 
typhoid  fever,  where  the  spleen  has  been  known  to 
weigh  fifteen  or  twenty  pounds. 

On  account  of  the  rich  blood  supply  an  injury  to 
the  spleen  causes  severe  hemorrhage,  which  the 
pulpy  condition  of  the  organ  renders  difficult  to 
check,  as  a  suture  usually  does  not  hold.  In  such 
accidents  the  whole  spleen  has  been  removed  with- 
out fatal  results.  Extirpation  of  the  spleen  is  also 
justified  in  certain  diseases  of  that  organ 


CHAPTER  IV. 
DIGESTIVE  SYSTEM. 

The  digestive  system  consists  of  alimentary  canal 
and  accessory  digestive  glands. 

The  Alimentary  Canal. — This  is  a  muscular  tube 
extending  through  the  body  and  measures  about 
thirty  feet  in  length.  The  following  parts  will  be 
described : 

I.  Mouth 
II.  Pharynx. 

III.  Esophagus. 

IV.  Stomach. 

V.  Small  Intestine. 

1.  Duodenum. 

2.  Jejunum. 

3.  Ileum. 

IV.  Large  Intestine. 

1.  Vermiform  Appendix. 

2.  Cecum. 

3.  Colon. 

(a)  Ascending. 

(b)  Transverse. 

(c)  Descending. 

(d)  Sigmoid  Flexure. 

4.  Rectum. 

THE  MOUTH. 

The  mouth  is  limited  by  the  lips  in  front,  and  the 
cheeks  laterally.     The  arched  palate  forms  its  roof 

136 


DIGESTIVE   SYSTEM. 


137 


and  the  tongue  is  attached  to  the  movable  floor, 
while  posteriorly  it  opens  into  the  pharynx  through 
the  isthmus  or  fauces.  This  cavity  is  lined  by  a  con- 
tinuous mucous  membrane,  consisting  of  stratified 
mucous  epithelium  placed  on  a  tunica  propria.  In 


Sinus  prcecervicalis. 


Fig.  99. — Human  embryo  of  about  twenty-eight  days  (His):  I-V, 
brain-vesicles;  /\  f\  /3,  /4,  cephalic,  cervical,  dorsal,  and  lumbar  flexures; 
ot,  otic  vesicle;  ol,  olfactory  pit;  mx^  maxillary  process;  h\  h2,  heart; 
/,  l\  limbs;  a  Is,  allantoic  stalk;  ch,  villous  chorion. 

the  submucosa  is  found  connective-tissue  elements 
in  which  the  elastic  fibers  predominate;  also  con- 
nective-tissue cells,  mucous  and  serous  glands, 
nerves,  and  nerve  endings,  blood-  and  lymph- vessels. 


138       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

The  mucous  membrane  is  continuous  with  the  skin 
at  the  outer  border  of  the  lips.  At  this  border  the 
horny  layer  of  skin  begins,  otherwise  the  skin  and 
this  mucous  membrane  are  similar  structures. 

Morphologically,  the  mouth  cavity  is  to  be  re- 
garded as  a  part  of  the  outside  surface  of  the  body, 
which,  embryologically,  has  been  included  by  the 
development  of  neighboring  parts.  At  the  time  the 
neural  folds  are  closing  dorsally  to  form  the  brain  and 
cord  there  develops  a  series  of  paired,  ventral, 
facial  pits.  These,  enumerated  from  before  back- 
wards, are:  the  lens  of  the  eye,  the  nasal  pit,  the 
mouth,  and  gill  clefts.  The  tissue  between  the  latter 
are  called  visceral  arches,  while  that  one  between  the 
anterior  gill  cleft  and  the  mouth  cavity  is  the  man- 
dibular  arch.  The  latter  is  morphologically  analogous 
to  the  visceral  arches.  In  man  the  gill  clefts  all 
finally  close  permanently,  but  the  ectodermal  em- 
bryonic mouth  cavity  ultimately  unites  with  the 
embryonic  foregut,  thus  forming  the  fauces  which 
lead  to  the  pharynx.  This  final  perforation  be- 
tween the  mouth  cavity  and  the  foregut  is  paired,  in 
lower  forms,  which  with  other  embryonic  relations 
confirms  the  view  that  the  mouth  cavity  morpho- 
logically represents  a  median  fusion  of  two  gill  clefts. 

During  this  period  of  development  the  forebrain 
grows  ventrally  and  the  mandibular  arch  grows  in  the 
same  direction.  The  space  between  these  structures 
is  the  beginning  of  the  mouth  and  the  nose,  and  is 
called  the  stomodeum.  At  this  time  a  rounded  eleva- 
tion, from  the  base  of  the  mandibular  arch,  grows  for- 
ward along  the  base  of  the  forebrain.  This  growth 


DIGESTIVE   SYSTEM. 


139 


forms  part  of  the  maxillary  arch,  and  finally  most  of 
the  upper  jaw.     In  this   manner  the  stomodeum 


Stomodeum. 


Nasal  pit. 

'Lateral  protuberance. 

•Globular  protuberance. 

•Maxillary  arch. 

^Mandibular  arch.         _  ^       ^  . ,,      m  _ 

•Nasal  process. 

•Nasal  pit. 

Lacrimal  canal. 

Maxillary  arch. 

Mandibular 
arch. 


Fig.  100. —  Development  of  the  face  of  the  human  embryo  (His): 
A,  Embryo  of  about  twenty-nine  days;  B,  embryo  of  about  thirty-four 
days;  C,  embryo  of  about  the  eighth  week;  D,  embryo  at  end  of  the 
second  month. 

becomes  divided  into  an  olfactory  region  and  the 
mouth  cavity  proper.     The  stomodeum  at  this  stage 


140       NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

is  a  deep  pentagonal  cavity.  Its  lower  boundary  is 
formed  by  the  mandibular  arch,  while  laterally  are 
to  be  found  the  maxillary  processes  of  each  side. 
Its  upper  boundary  is  formed  by  an  unpaired  growth 
called  the  nasofrontal  or  nasal  process  (Fig.  100.) 
Situated  on  each  side  of  the  nasal  process  are  the 
nasal  pits.  Each  pit  divides  the  nasofrontal  process 
into  a  lateral  external  portion  called  the  lateral 
frontal  protuberance ,  which  forms  the  outer  boundary 


Ventricle  of  cerebrum. 


Place  from  which  the  hy- 
pophysis is  developed. 

Stomodeum. 


Heart. 
Pore  gut. 
Notochord.  • 


Third  ventricle. 


Fourth  ventricle. 


Spinal  cord. 


Fig.  10 1. —  Median  section  through  the  head  of  an  embryo  rabbit 
6  mm.  long  (after  Mihalkovics) 

of  each  nasal  pit,  and  a  median  or  central  portion 
called  the  globular  protuberance,  which  constitutes 
the  inner  boundary  of  each  pit.  The  two  lateral  or 
side  protuberances  grow  around  the  olfactory  pits 
and  form  the  alse  of  the  nose,  while  the  two  central 
portions  develop  into  the  intermaxillary  bone  con- 
taining the  incisor  teeth  and  the  center  of  the  lip. 
By  studying  the  text  figures  a  correct  idea  of  these 


DIGESTIVE  SYSTEM. 


141 


relations  is  readily  obtained.  It  will  be  seen  that 
the  line  of  contact  between  each  lateral  protuberance 
and  maxillary  process  forms  a  groove,  the  naso-optic 
furrow  or  lacrimal  groove,  which  later  closes  to  form 
the  lacrimal  canal.  The  line  of  contact  between 
each  globular  protuberance  and  the  maxillary  pro- 
cess is  less  close,  and  places  each  nasal  pit  in  wide 
communication  with  the  mouth.  A  failure  of  union 
in  the  latter  case  causes  the  deformity  of  harelip, 


Median  triangular  por- 
tion of  palate. 

Dental  ridge. 


Lateral  portion  of 
palate. 


Fig.  102. —  Roof  of  the  oral  cavity  of  a  human  embryo  with  the  fun- 
daments of  the  palatal  processes  (after  His). 

which    may   be    double    or    single,    depending   on 
whether  both  or  only  one  side  is  involved. 

About  the  fortieth  day,  in  the  human  embryo,  the 
maxillary  processes  have  grown  so  far  toward  the 
median  plane  that  they  have  met  and  united  with 
the  lateral  and  also  the  median  protuberances  of  the 
nasofrontal  process.  The  nasal  pits  are  thus  sepa- 
rated externally  from  the  oral  fossa.  With  this 
union  the  arch  of  the  upper  jaw  is  complete,  but  the 


142       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

inclosed  space  is  in  one  chamber,  there  being  no 
separation  between  the  mouth  and  nose  cavities. 
The  formation  of  a  palate,  however,  effects  a  separa- 
tion between  the  two.  The  rudiments  of  the  palate 
appear  as  shelf-like  projections  from  the  inner  or 
oral  surface  of  the  upper  jaw.  A  triangular  piece 
grows  backward  from  the  globular  protuberance  of 
the  nasofrontal  process,  which  ultimately  unites 
with  horizontal  or  palatal  plates  from  the  maxillary 
arch.  In  the  eighth  week  of  embryonic  life,  union  of 
the  palatal  plates  begins  at  their  anterior  extremi- 
ties and  proceeds  backward.  A  deficiency  in  the 
union  constitutes  the  deformity  of  cleft  palate. 
Cleft  palate  is  therefore,  embryologically,  a  later 
development  than  harelip.  Either  may  occur  with- 
out the  other,  but  they  are  usually  found  together. 
The  cleft  of  the  palate  usually  turns  to  one  side, 
passing  out  between  the  cuspid  and  lateral  incisor 
teeth.  A  double  cleft  palate  is  Y-shaped,  the 
center  piece  in  front  containing  the  incisors,  and 
representing  the  anterior  triangular  piece  of  the 
rudimentary  palate,  this  piece  having  failed  to  unite 
with  the  lateral  palatine  plates.  This  deficiency 
may  involve  the  hard  or  the  soft  palate,  or  it  may 
affect  both,  and  even  produce  a  cleft  or  bifid  uvula. 

The  completion  of  the  palate  definitely  separates 
the  nasal  chambers  from  the  mouth,  the  only  com- 
munication between  the  two  being  through  the 
posterior  nares..  The  permanent  limitations  of  the 
mouth  are  thus  established  from  a  cavity  that 
develops  primarily  as  an  ectodermal  invagination. 
The  ectoderm  invests  not  only  the  mouth  proper, 


DIGESTIVE  SYSTEM. 


143 


but  clothes  at  least  the  anterior  portion  of  the  adult 
pharynx.     The  tongue,  however,  is  invested  with  en- 
toderm  epithelium  and 
§o  are  the  Eustachian 
tubes. 

TEETH. 

Morphologically, 
teeth  are  appendages 
of  the  skin,  and  are  to 
be  compared  with  such 
structures  as  hair  and 
nails.  They  are  thus 
a  part  of  the  exoskel- 
eton  and  their  relation 
to  the  bones  or  the  en- 
doskeleton  is  entirely 
a  secondary  process, 
for  the  purpose  of 
strength  and  support. 
In  many  of  the  fishes 
the  mouth  generally 
is  lined  by  simple  cone- 
shaped  teeth  that  serve 
the  purpose  of  seizing 
and  holding  the  ani- 
mal's prey.  In  man 
the  additional  function  of  masticating  the  food  has 
greatly  modified  the  form  and  structure  of  teeth. 

Dentition. — There  are  twenty  deciduous  or  tem- 
porary teeth  that  erupt  between  the  ages  of  six 
months  and  two  and  one-half  years.  In  each  jaw 
these  are, — incisors  4,  cuspids  2,  molars  4,  the  dental 


Fig.  103. —  The  palate  and  supe- 
rior dental  arch  (right  side):  i,  Me- 
dian incisors;  2,  lateral  incisors;  3, 
canine;  4,  first  bicuspid;  5,  second 
bicuspid;  6,  first  molar;  7,  second 
molar;  8,  wisdom-tooth;  9,  mucous 
membrane  of  the  hard  palate  con- 
tinuous behind  with  that  of  the  soft 
palate;  10,  the  anteroposterior  raphe 
of  palate;  n,  pits  on  each  side  of  the 
raphe  perforated  with  the  orifices  of 
glands;  12,  anterior  rugosities  of  the 
mucous  membrane  (after  Testut). 


h  W  W  > 

<  a  ex  j 
S        *  P 

IjSSl" 

rtrtd                        rt                      rt^rtrt 
oJojOj                             D                           4)l>o;qj 

files'" 

t^              t^         .      CX3 

1 

h  W  W     . 

<  a  tA  Q 

2  5  h  £ 

«  5  »  05 

£|HW 

JS            J          ^3         ^3                  ^J3                       X     J=     J3            X 

C             "C"CC                  *^G                        c'CG              C 
O              OOO                   0O                        OOO              O 

££££            °£££££ 

M          M          (|                  ro                           CNICSCNCO 

S 

<  a  W  £  w 

03  H  Z  £  (* 

X-*                                             .               .X^     . 

1 

|1|§| 

-s                              -s 

PH   !> 

T 

o 
w 

gfifsj 

|.| 

5 

l^|s 

M      -^- 

HH 

Pll3j 

2 

W 

o^  w^< 

.      .         .          ..           .         . 

o 

i|j  b  J 

g 

o 

<B  J  A    . 

ij 

3 

Ipll 

.     .       •.       S         .... 

§ 

(jj  BJ  , 

o 

Q 

Q   ^?2   « 

xl$ 

W 

13 

o  a  w  tti  M 

....  II   .... 

O 

S  S 
5  h  Q 

°£o 

a 

O 
O 

a  a  < 

X 

"3. 

w 

w 

fcco 

' 

u 

0  W 

.5        .5        •-     .5         w     ^     °         o   '     o         o 

P 

i/5  w 
w  a 

/-V     1_ 

^  1=  S  jH  1  i  J1  51  J1  I1 

•uoppuap  XaBaodtuax 

144 


:   :     :     I| 

M<cd 

....    H^ 

1     1 

.C 

1 

•j 

;;;;!. 

1 

w                        <^ 

:   :     :     1 

H 

^ 
A 

J-^                      r!  >-< 

SI      "^ 

>»                     <u  •* 

$        <s 

£.* 

a; 

4) 

1 

t     It 

$i 

•  •   •  ij 

=<« 

....  1 

•5 

to 

l_ 

6 

rO                      -—  ^^% 

o  £  5 

bfi 
**  g  cd  en                        ~  ctf 

"oSort                   ^.S 
-c^g-o                   .ti  S 
o  S  |  S                   w  * 
w 

si      ^s 

£i^2        ^12 
o  SjH        o  S.2 
-o  «  §        -o  fc  2 
§*e         o^E 
°  2            Ui« 

^ 

^  ^  ^    t  ^_  ^ 

c 

•-  •   •§   -5  *  -g   i 

s:  i:  2:3  :  |:  |: 

i  :  i  -'  1  :  1  •' 

^.2 

c   '     -2     *J  '     '5,     & 
^   .     "rt     ^~~         ^     w 

.   (/)         •—  '             .    c/j          y 

O.-r;      ^.T       O,-r.      ^r       D, 
3            ^        3            ^        3 

^d    ^d  "So,    §*d  ^  '    &  ' 

tn^     to  "    TJ  "    -g0      w"2     «^ 

•  .    d  -   ^  •    d  - 
.£  m     55  w    .5  M     ^  m 
*       ^       ^       JS 

cs            W            rO          CO 

145 


146       NORMAi,   HISTOLOGY   AND   ORGANOGRAPHY. 

formula  for  one  side  being, — 1.|-  C.^j-  M.f  =  10.    The 
second  set,  or  permanent  teeth,  number  thirty-two 


'•"•Enamel. 


Pulp  cavity. 


-Dentm. 


Cementum. 


w 

Jp/ 

Fig.  104. —  Scheme  of  a  longitudinal  section  through  a  human 
tooth.  In  the  enamel  are  seen  the  "lines  of  Retzius"  (Bohm  and 
Davidoff). 


PLATE  II. 

DISSECTED  SKULLS  SHOWING  THE   DEVELOPMENT  OF  THE  TEETH 
(Noyes). 

1.  Skull  at  nine  months,  central  incisoFS  just  erupted,  laterals  not  yet 
through  the  gum.     The  root  of  the  central  about  half  formed.     The 
lower  first  and  second  temporary  molars  seen  in  their  crypts.     The  crypt 
for  the  lower  first  permanent  molar  shown,  but  the  developing  tooth  has 
dropped  out  of  it.     The  upper  temporary  cuspid  and  first  and  second 
molars  are  seen  in  their  crypts.     Notice  the  straightness  of  the  lower  jaw. 

2.  Skull  at  one  year.     Two  incisors  in  each  jaw  are  erupted.     The 
first  molars  are  just  starting.     Notice  the  formation  of  the  root  of  the 
lower  temporary  molars  just  beginning.     Also  notice  the  first  permanent 
molar  in  its  crypt  with  half  of  the  crown  formed. 

3.  Skull  in  the  second  year.     The  temporary  first  molar  dnd  cuspid 
partly  erupted.     Notice  the  development  of  their  roots.     Notice  the  per- 
manent cuspid  above  and  me  first  molar  below  in  their  crypts. 

4.  Skull  in  fourth  year.     Complete  temporary  dentition.     Notice 
the  upper  central,    lateral   cuspid    and    bicuspid    in    their  crypts;    the 
lower  incisors,  cuspid,  first  bicuspid,  and  first  permanent  molar. 

5.  Skull   in   sixth  year.     Complete   temporary   dentition   with   the 
first  permanent  molar  in  place.     The  lower  central  incisors  have  just 
beenjost  and  the  permanent  ones  are  just  coming  through  the  gum.    The 
cuspids,  bicuspids  and  second  molar  are  seen  in  their  crypts. 

6.  The  left  side  of  the  same  skull  as  No.  5.     Notice  the  extent  to 
which  the  roots  of  the  first  permanent  molar  are  developed. 

7.  Front  view  of  the  same  skull  as  No.  6.    Notice  the  position  of  the 
incisors  and  cuspids  in  their  crypts. 

8.  Skull  in  seventh  year.     The  toothless  age.     Upper  incisors  lost 
and  the  permanent  ones  not  erupted.     One  lower  incisor  in  place.    First 
permanent  molar  in  place,  but  the  roots  not  fully  formed.     Crown  of  the 
second  permanent  molar  seen  in  its  crypt 


PLATE  u. 


PLATE  III. 

DISSECTED  SKULLS  SHOWING  THE  DEVELOPMENT  OF  THE  TEETH — 
Continued  (Noyes). 

9.  Skull  in  eleventh  year.     The  incisors  are  in  position,  but  the  tem- 
porary molars  and  cuspids  are  still  in  position.     The  second  permanent 
molar  is  through  the  bone  but  not  through  the  gum. 

10.  The  left  side  of  the  same  skull.     On  this  side  the  lower  tem- 
porary cuspid  and  first  molar  have  been  lost.     Note  the  position  of  the 
upper  cuspid  in  these  pictures  and  the  distance  the  root  extends  toward 
the  orbit.     The  lateral  on  the  left  side  is  not  of  typical  form,  but  is  a 

'peg  tooth." 

11.  Skull  in  the  thirteenth  year.     The  lower  second  molar  the  only 
remaining  temporary  tooth.     The  second  permanent  molar  is  in  place 
but  the  roots  are  not  fully  developed.     The  crypt  for  the  third  molar 
(wisdom  tooth)  is  seen. 

12.  Skull  of  young  adult.     The  upper  centrals  are  broken.     The 
second  molars  are  fully  developed  and  the  third  molar  shows  the  crown 
fully  formed  in  the  crypt. 

13.  Skull  of  adult.     This  shows  the  full  permanent  dentition  and 
the  roots  of  the  teeth. 

14.  Edentulous  jaws.     Notice  the  position  of  the  mental  foramen. 


PLATE  III. 


•    .  '    i 


DIGESTIVE   SYSTEM.  147 

and  in  each  jaw  are  divided  into, — incisors  4,  cus- 
pids 2,  bicuspids  4,  molars,  6,  the  dental  formula  for 
one  side  being,— I.f  C.I  B.f  M.f  =  16. 

Structure  of  Teeth. — The  parts  of  a  tooth  are 
crown,  neck,  roots  and  pulp.  Its  calcareous  wall 
consists  of  enamel,  dentin,  and  cementum. 

Enamel. — The  enamel  is  the  hardest  tissue  in  the 
body  and  covers  the  exposed  portion,  or  crown,  of 
the  teeth.  Its  function  is  to  mechanically  protect 
the  tooth.  This  enamel  is  derived  from  the  ecto- 
derm, while  all  bone  tissues  are  products  of  the 
mesoderm.  Bone,  if  injured,  may  regenerate  and 
repair  the  defect.  Enamel  does  not  regenerate  if 
injured,  the  defect  being  permanent,  as  the  formative 
enamel  tissue  disappears  before  the  eruption  of  the 
tooth.  Chemically,  it  is  composed  of  phosphates 
and  carbonates  of  calcium  and  magnesium,  a  small 
amount  of  fluorides,  water,  and  perhaps  a  very  small 
amount  of  organic  material.  In  consequence  of  the 
latter,  enamel,  unlike  bone,  is  soluble  in  acids, 
leaving  scarcely  any  residue. 

Enamel  is  composed  of  two  structural  elements,— 
(a)  enamel  rods  or  prisms  (also  called  fibers) ,  and  (6) 
inter  prismatic  or  cement  substance^  both  of  which  are 
calcified.  These  elements  have  different  properties, 
both  chemical  and  physical.  The  interprismatic 
substance  is  more  readily  acted  upon  by  acids,  and 
it  is  therefore  possible  to  etch  enamel  sections  and 
produce  a  disassociation  of  the  enamel  rods.  The 
interprismatic  substance  is  not  so  strong  as  the  rods, 
and  in  splitting  or  breaking  the  enamel  the  tissue 
usually  separates  along  the  cement  lines;  that  is, 


14^       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

these  lines  form  paths  of  least  resistance,  a  fact  taken 
advantage  of  in  operative  dentistry. 

According  to  Noyes  ("Dental  Histology"),  "the 
enamel  rods,  or  prisms,  are  long,  slender  prismatic 
rods  or  fibers,  five-  or  six-sided,  pointed  at  both  ends, 
and  alternately  expanded  and  constricted  through- 
out their  length.  They  are  from  3,4  to  4.5  microns 
in  diameter,  some  of  them  apparently  reaching  the 
entire  distance  from  the  surface  of  the  dentin  to  the 
surface  of  the  enamel,  but,  as  the  diameter  of  the 
rods  is  the  same  at  their  outer  and  inner  ends,  and 

as  the  crown  surface  is 
much  greater  than  the 
surface  of  dentin  cov- 
ered by  enamel,  there 
are  many  rods  that  do 
not  extend  through 
the  entire  thickness. 
These  short  rods  end 

Fig.   105. — a,   Enamel  rods  in  cross 

section;    by  Enamel    rods,  longitudinal      in  tapering  points  be- 
tween the  converging 

rods,  which  extend  the  entire  distance.  To  ex- 
press this  in  terms  of  development,  as  the  forma- 
tion of  enamel  begins  at  the  surface  of  the  dentin, 
the  increasing  area  of  crown  surface  requires  more 
ameloblasts,  and  as  new  ameloblasts  take  their 
places  in  the  layer  the  formation  of  new  enamel  rods 
begins  between  the  rods  which  were  previously 
forming.  These  short  rods  are  most  numerous  over 
the  marginal  ridges  and  the  points  of  the  cusps." 

The  rods  are  not  perfectly  smooth  and  even,  but 
show  alternately  expansions  and  constrictions. 


DIGESTIVE   SYSTEM.  149 

They  are  so  arranged  that  the  expansion  of  adjacent 
rods  lie  opposite  each  other;  that  is,  the  expansions 
do  not  interlock  with  the  constrictions.  The  cement 
substance,  therefore,  has  a  reciprocal  arrangement. 
Sections  ground  parallel  to  the  rods  show,  therefore, 
dark  and  light  lines,  described  as  the  striations  of  the 
enamel,  which  are  caused  by  the  difference  in  the 
refracting  power  of  the  prismatic  and  interprismatic 
substances.  In  a  ground  section  across  the  rods,  the 
tissue  presents  a  mosaic  pattern,  which  becomes 
more  distinct  if  treated  with  acid. 


Fig.  106. —  Transverse  section  of  enamel  (Noyes). 

Lines  of  Retzius. — These  lines  or  stratification 
bands  begin  at  the  tip  of  the  dentin  cusps  and  sweep 
around  in  larger  and  larger  zones.  They  thus  pass 
obliquely  through  the  enamel  and  record  the  growth 
of  the  crown,  as  each  line  was  at  one  time  the  surface 
of  the  enamel.  They  are  to  be  regarded  as  traces 
of  the  strata  caused  by  the  periodic  deposition  of 
lime  salts. 

According  to  Noyes,  "the  appearance  of  striation 
is  the  record  in  the  fully  formed  tissue  of  the  manner 


150       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


of  growth,  each  dark  stripe  or  expansion  in  a  rod 
representing  a  globule  of  calcified  material.  The 
ameloblasts  build  up  the  rods  by  the  addition  of 
globule  after  globule,  surrounding  them  with  a 
cementing  substance  and  completing  the  calcifi- 
cation of  both.  In  this  sense  the  striation  of  the 
enamel  may  be  said  to  record  the  growth  of  the  in- 
dividual rods." 

Direction  of  the  En- 
amel Rods. — Upon  the 
axial  surface  the  rods 
are  usually  straight 
and  parallel  with  each 
other,  but  upon  the  oc- 
clusal  surface  they 
change  their  direction 
by  a  series  of  sym- 
metrical curves,  and 
often  become  much 
twisted  and  wound 
around  each  other,  par- 
ticularly the  inner 
ends.  In  operative 
dentistry  it  is  found 
that  the  enamel  upon  the  axial  surface  cleaves 
readily  while  the  gnarled  portion  upon  the  occlusal 
surface  tends  to  break  away  in  chunks. 

Fig.  no  shows  the  general  plan  of  the  arrange- 
ment of  the  enamel  rods  in  the  formation  of  the 
crown.  In  the  gingival  half  of  the  middle  third  the 
rods  are  horizontal.  Their  inclination,  from  this 
horizontal  direction,  gradually  increases  toward  the 


Fig.  107. — Tip  of  an  incisor, 
showing  lines  of  stratification  of  the 
enamel  (Noyes). 


DIGESTIVE   SYSTEM.  151 

root  and  toward  the  occlusal  surface,  so  that  at  the 
apices  of  the  latter  surface  the  rods  are  placed 
vertical  to  a  horizontal  plane.  Because  of  this  plan 
Noyes  divides  all  cavities,  in  dental  work,  into  two 
classes : 

"i. — Those   in   which  the   enamel  rods   are  in- 


Enamel. 


Enamel. 


Den/in. 


Dentin. 


Fig.     108. — Straight     enamel,  Fig.     109.  —  Gnarled    ^enamel. 

showing  dento-enamel  junction  showing  dento-enamel  junction 
(Noyes).  (Noyes). 

clined  toward  the  cavity,  characteristic  of  the  oc- 
clusal surfaces. 

"  2. — Those  in  which  the  enamel  rods  are  inclined 
away  from  the  cavity,  characteristic  of  axial  sur- 
faces" (Fig.  in). 

In  preparing  cavities  on  the  axial  surfaces  the 


152       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY, 

lateral  walls  should  be  beveled,  as  shown  in  the  above 
figure.  The  historic  requirements  for  strength  in 
enamel  walls  are : 

1.  The   enamel  must  be  supported  upon   sound 
dentin. 

2.  The  rods  which  form  the  cavo-surface  angle 
must  run  uninterruptedly  to  the  dentin. 

3.  They  must  be  supported  by  short  rods,  with 


Enamel  rods  horizontal 


:-.  Dento-enamel  margin. 
Enamel. 


Fig.   no. —  Drawing,  showing  the  direction  of  the  rods  over  the  mesial 
marginal  ridge  of  a  bicuspid  (Noyes). 

their  inner  ends  resting  on  the  dentin  and  their 
outer  ends  abutting  upon  the  cavity  wall,  where  they 
will  be  covered  by  the  filling  material. 

4.  That  the  cavo-surface  angle  be  cut  in  such  a 
way  as  not  to  expose  the  ends  of  the  rods  to  fracture 
in  condensing  the  filling  material  against  them. 

"The  first  step  in  the  preparation  of  an  enamel 
wall  is  to  determine  the  direction  of  the  enamel  rods 
by  cleavage  with  a  chisel  or  hatchet.  Then  the  wall 


DIGESTIVE  SYSTEM. 


153 


Rods  inclined  away 
from  cavity. 


Enamel. 


Rods  inclined  toward  camty. 
Fig.  in.— Illustrating  the  two  classes  of  cavities  (Noyes). 


Dentin. 


Enamel- 


Fig.  ii2.—  Labio-lingual  section   of  superior  lateral   incisor,    showing 
a  pit  cavity  (Noyes). 


154       NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 


must  be  smoothed  or  trimmed  by  a  shaving  motion 
of  the  chisel,  increasing  the  inclination  of  the  wall 
slightly.  This  is  done  so  as  to  be  sure  and  reach  the 
rod  directions  and  remove  the  portions  of  the  tissue 
that  has  been  splintered  by  the  cleavage.  Then  the 
cavo-surface  may  or  may  not  be  trimmed,  as  the 
position  demands"  (Fig.  in,  Noyes). 


—  Enamel. 


._  Branching  of 
the  dentinal 
tubules. 


Dentinal  tubules 


Interglobular 
space. 


Fig.  113. —  A  portion  of  a  ground  tooth  from  man,  showing  enamel 
and  dentin  (Bohm  and  Davidoff). 

Grooves,  fissures,  pits  and  developmental  lines 
are  points  of  weakness  and  in  operative  work  cavi- 
ties must  be  excavated  so  as  to  establish  a  strong 
margin,  histologically,  against  which  to  pack  the 


DIGESTIVE   SYSTEM.  155 

filling.  The  arrangement  of  the  enamel  rods  must 
therefore  be  constantly  borne  in  mind  in  the  opera- 
tive repair  of  teeth. 

Dentin. — The  dentin  is  the  second  layer  of  teeth, 
and  not  only  makes  up  the  mass  of  a  tooth  but  de- 
termines its  form;  that  is,  the  number  of  cusps  and 
roots  is  moulded  by  the  developmental  process  of  the 
dentin.  Its  histologic  form  has  much  to  do  with  the 
penetration  of  caries. 

Dentin,  like  bone,  develops  from  the  mesoderm, 
and  consists  of  an  organic,  formative  matrix  impreg- 
nated with  about  72  per  cent,  of  inorganic  salts.  On 
boiling  it  yields  gelatin.  Minute  canals  of  dentinal 
tubules  radiate  from  the  central  cavity  of  the  tooth, 
which  contains  the  formative  organ  or  pulp.  These 
tubules  are  from  i.i  to  2.3  microns  in  diameter  and 
are  separated  from  each  other  by  a  dentinal  matrix  of 
about  10  microns  in  diameter.  In  the  crown  the 
tubules  branch  but  little,  excepting  close  to  the  en- 
amel where  they  anastomose  freely.  In  the  crown 
they  radiate  in  sweeping  curves  so  as  to  open  at 
right  angles  on  the  dentinal  surface.  This  produces 
"s"  or  "f  "-shaped  curves  known  as  primary  curves. 
They  also  present  many  wavy  curves  known  as 
secondary  curves,  which  is  really  the  result  of  an  open 
spiral  course  taken  by  the  tubules.  In  the  body  of 
the  dentin  a  few  small  branches  are  given  off  at 
acute  angles,  but  near  the  enamel  junction  the  tu- 
bules fork  and  branch  freely,  forming  an  anasto- 
mosis that  facilitates  in  the  spreading  of  caries  just 
beneath  the  enamel,  the  micro-organisms  diffusing 
sideways  and  then  penetrating  the  dentin  in  the 
direction  of  the  tubes. 


156      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


In  the  root  the  tubules  radiate  directly  to  the  ce- 
mentum,  showing  only  the  primary  curves.  Many 
fine  branches  pass  in  all  directions  from  tubule  to 
tubule.  The  dent  in  next  to  the  cementum  contains 
many  small  irregular  spaces  that  connect  with  the 
dentinal  tubules.  They  present  a  granular  ap- 
pearance in  ground  sections,  and  are  therefore 
called  the  granular  layer  of  Tomes.  These  spaces  are 
filled  by  the  enlarged  ends  of  the  dentinal  fibrils, 
which  are  cell  processes  of  the 
odontoblasts ,  while  the  fibrils 
also  fill  the  dentinal  tubules. 
The  layer  of  Tomes  may  some- 
times be  found  beneath  the 
enamel,  but  is  never  well 
marked. 

The  dento-enamel  junction 
presents  rounded  projections. 
This  scalloped  appearance  has 
given  rise  to  the  view  that 
certain  dentinal  tubules  pass 
for  a  short  distance  into  the 
enamel.  In  ground  sections, 
irregularly  branched  dentinal 
spaces  are  often  found  at  a  uniform  depth  from  the 
surface.  These  are  the  inter  globular  spaces  of  Czer- 
mak  and  represent  areas  of  imperfectly  developed 
dentin.  Lastly,  the  sheaths  of  Neumann  represent 
the  inner  wall  of  the  dentinal  tubules,  and  may  be 
regarded  as  differentiated  and  more  resistant  ground 
substance. 

The  formation  of  dentin  continues  for  an  indef- 


Fig.  114. —  Section  of  den- 
tin at  right  angles  to  the 
tubules  (Noyes). 


DIGESTIVE   SYSTEM. 


157 


inite  period  after  the  eruption  of  a  tooth.  The  proc- 
ess is  one  of  apposition,  thickening  the  dentin  at  the 
expense  of  the  pulp.  Finally  this  growth  ceases. 
Irritation  of  the  pulp,  or  the  pulp  of  some  tooth  on 
the  same  side,  may  lead  to  the  formation  of  second- 
ary dentin.  The  latter  is  an  imperfect  structure. 
The  tubules  are  smaller  and  less  numerous,  while  the 
matrix  is  less  compact  and  shows  a  deficiency  of 


111; 


sill 


Dento-enamel 


Dentin. 


£  Dentinal 
tubules. 


Fig.   115. —  Section  of  dentin  in  the  crown  cut  in  length  of  the  tubules 

(Noyes). 


inorganic    salts.     Several    deposits    of    secondary 
dentin  may  thus  be  produced. 

The  Pulp. — The  pulp  occupies  the  center  of  the 
tooth.  It  consists  of  connective-tissue  cells,  con- 
nective-tissue fibrils,  a  semifluid  interfibrillar  ground 
substance,  nerve  plexus  largely  non-medullated, 
blood  and  lymph  vessels.  We  may  recognize  three 
kinds  or  layers  of  cells,  the  most  important  being  the 


158       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

odontoblasts,  forming  the  outer  surface  of  the  pulp 
next  to  the  dentin. 

i.  The  odontoblasts  form  a  continuous  layer  over 
the  entire  pulp  surface,  being  everywhere  in  contact 
with  the  dentin.  This  layer  has  been  called  the 


Enamel  pulp. 


Enamel  cells. 


-  Odontoblasts. 


Fig.  1 1 6. — A  portion  of  a  cross  section  through  a  developing  tooth 
(Bohm  and  Davidoff).  The  dentin  is  formed,  but  has  become  homo- 
geneous from  calcification.  Bleu  de  Lyon  differentiates  it  into  zones 
(a  and  b).  At  c  is  seen  the  intimate  relationship  of  the  odontoblasts 
to  the  tissue  of  the  dental  pulp. 

membrane  eboris  or  the  "membrane  of  ivory."  The 
odontoblasts  are  mesoderm  cells,  columnar,  some- 
times club-shaped,  with  basal  nuclei  and  three 
kinds  of  processes,  (i)  Each  cell  has  one  to  three 
long,  slender,  protoplasmic  processes  projecting  into 


DIGESTIVE   SYSTEM.  159 

the  dentinal  tubules,  and  extending  through  the 
tubule  to  the  outer  surface  of  the  dentin,  where  they 
completely  fill  the  granular  spaces  already  described 
as  the  granular  layer  of  Tomes.  It  is  generally 
believed  that  these  processes  may  transmit  im- 
pressions to  the  sensory  nerves  of  the  pulp.  (2) 
Each  odontoblast  shows  lateral  processes,  minute 
but  blunt,  that  interlock  with  like  processes  from 
adjacent  cells.  (3)  Usually  a  single  process  pro- 
jects from  the  basal  end  into  the  pulp. 

The  odontoblasts  are  dentin-forming  cells  and 
superintend  the  formation  and  calcification  of 
primary  and  secondary  dentin. 

2.  The  layer  of  Weil  represents  a  layer  of  connec- 
tive-tissue cells  forming  a  thin  zone  just  beneath  the 
odontoblasts.     In  thin  sections  this  appears  as  a 
thin  layer  about  half  as  thick  as  that  of  the  odonto- 
blasts. 

3.  Underneath  the  layer  of  Weil  the  connective- 
tissue  cells  are  numerous  and  closely  packed.     To- 
ward the  center  of  the  pulp  they  become  loosely  but 
uniformly  scattered.     The  cells  are  small,  have  a 
single   deep-staining    nucleus,   and   the    cytoplasm 
stretching  out  into  slender  processes  in  many  direc- 
tions, forming  stellate  cells ;  or  in  two  directions  to 
form  spindle  cells. 

The  connective-tissue  fibrils  of  the  pulp  are  similar 
to  those  of  white  fibrous  connective  tissue,  sometimes 
resembling  the  reticular  variety.  The  vascular  con- 
dition of  the  pulp  makes  it  an  organ  of  nourishment 
for  the  dentin  as  well  as  the  mature  tooth. 

Cementum. — The  cementum  covers  the  dentin  in 


160       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

the  root  portion  of  a  tooth.  At  the  gingival  margin 
it  slightly  overlaps  the  enamel.  Near  this  margin  it 
forms  a  thin  layer,  but  becomes  thicker  toward  the 
apex  of  the  root  and  between  the  roots  of  the  bi- 
cuspids and  molars.  The  cementum  consists  of 
parallel  lamellae  of  bone  tissue  that  contain  no 
Haversian  canals.  Small  blood-vessels  from  the  in- 
vesting peridental  membrane  penetrate  the  lamellae, 
while  other  small  vessels  from  the  pulp  pass  through 


Cemen  turn. 


Den  tin.  < 


Fig.   117. —  Cross  section  of  human  tooth,  showing  cement  and  dentin. 
At  a  are  seen  small  interglobular  spaces  (Tomes'  granular  layer). 

the  cementum  in  the  opposite  direction.  Fibers 
from  the  investing  peridental  membrane  find  attach- 
ment in  the  cementum.  These  fibers  resemble  the 
fibers  of  Sharpey  in  bone.  The  cementum,  there- 
fore, furnishes  a  medium  of  attachment  by  which  the 
tooth  is  held  in  position. 

Cementum  is  constantly  being  produced  by  the 
apposition  of  new  surface  layers.     In  newly  erupted 


DIGESTIVE   SYSTEM.  l6l 

teeth  the  cementum  is  thin  and  in  teeth  of  old  per- 
sons the  cementum  is  thick.  This  continuous 
growth  is  necessary  in  order  to  establish  attachment 
for  new  fibers  of  the  peridental  membrane  and  to  con- 
form to  the  natural  growth  of  the  jaw. 

Between  the  lamellae,  particularly  in  the  apical 
portion  of  the  root  where  the  cementum  is  thick, 
numerous  lacunae  are  present,  resembling  those  of 
bone.  Canaliculi  radiate  from  these  lacunae  with 
less  regularity,  however,  than  in  the  case  of  bone. 
They  may  be  confined  to  one  side  of  a  lacuna,  usually 
the  side  toward  the  surface. 

Local  thickenings  of  the  cementum,  called  hyper- 
trophies, are  common.  These  enlargements  involve 
one  or  more  of  the  lamellae  and  were  formerly  called 
exostoses,  or  cementostoses. 

Peridental  Membrane. — This  is  an  organic  tissue 
that  surrounds  the  root  of  teeth  and  occupies  the 
space  between  the  cementum  and  the  bony  wall 
of  the  alveoli.  Its  chief  function  is  to  anchor  a  tooth 
to  the  jaw  and  give  support  to  the  gingivus.  Its 
chief  constituent  is  white  connective-tissue  fibers  in- 
terspersed with  a  variety  of  cells,  blood-vessels, 
lymphatics  and  nerves. 

The  fibrous  tissue  may  be  divided  into  two  classes : 
coarse,  radiating  fibers  that  form  the  principal  bulk 
and  perform  the  principal  function  of  anchorage,  and 
a  secondary  fine  variety  that  interlace  with  these  and 
unite  largely  with  the  anastomosing  blood-vessels  of 
the  tissue.  The  principal  fibers  connect,  on  the  one 
hand,  with  the  cementum  which  they  enter  in  bun- 
dles to  form  the  fibers  of  Sharpey,  and  on  the  other 


1 62      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


hand  they  unite  with  the  periosteum  of  the  bony 
alvoli  and  the  subepithelial  tissue  of  the  gum.  From 
the  upper  portion  of  the  cementum  these  fibers  pass 
horizontally,  some  of  them  directly  to  connect  with 
the  cementum  of  adjacent  teeth  and  others  to 
mingle  with  the  connective  tissue  of  the  adjacent 
mucous  membrane,  thus  giving  a  firm  support  to  the 


Muscle  fibers. 


Periosteum. 

Bone  of  alveolar 

Process. 
Peridental  mem-^j^ 

brane. 


Fig.  1 1 8. — Transverse  section  of  pe 
portion  (N< 


ibrane  in  alveolar 


>yes;. 


gingivus,  a  condition  which  becomes  of  primary  im- 
portance in  the  mastication  of  food.  The  fibrous 
mat  of  the  gum  is  usually  greater  on  the  lingual  side, 
where  food  is  brought  against  the  gingivus  with  con- 
siderable force.  If  a  crown  band  is  extended  too  far, 
or  if  deposits  accumulate  as  in  case  of  uncared-for 


DIGESTIVE   SYSTEM.  163 

teeth,  these  supporting  fibers  will  be  cut  off  and  the 
gingivus  drops  down  and  no  longer  fills  the  inter- 
proximal  space. 

In  the  alveolar  portion  the  principal  fibers  not 
only  spread  out  and  radiate  like  a  fan,  but  are  in- 
clined downward  from  their  attachment  in  the  ce- 
mentum  to  their  anchorage  in  the  bony  wall  of  the 
alveolus.  Some  of  these  fibers  are  tangential  to  the 
cementum  and  thus  support  the  tooth  against  a 
rotary  strain.  The  principal  fibers  thus  perform  a 
physical  function  and  firmly  bind  the  tooth  to  the 
adjacent  hard  and  soft  tissues.  At  the  alveolar 
border  and  at  the  apex  of  the  root  they  are  so  ar- 
ranged as  to  support  the  tooth  against  lateral 
strain,  while  in  the  rest  of  the  alveolar  portion  the 
tangential  fibers  are  particularly  numerous  and  sup- 
port the  tooth  against  any  rotary  force  which  may 
result  from  the  mastication  of  food.  At  the  gingivus 
line  the  fibers  blend  with  the  submucosa  and  bind 
the  gum  closely  to  the  neck  of  the  tooth.  At  the 
apex  of  the  root  the  secondary  loose  variety  becomes 
continuous  with  the  connective  tissue  of  the  tooth 
pulp. 

The  cellular  elements  of  the  peridental  membrane 
are  the  fibroblasts,  cementoblasts,  osteoblasts,  osteo- 
clastsy  and  epithelial  cells,  which  have  been  called  the 
glands  of  the  peridental  membrane.  All  these  cells 
are  interposed  between  the  bundles  of  supporting 
fibers  already  described. 

i.  The  fibroblasts  are  spindle-shaped  connective- 
tissue  cells  arranged  in  radiating  rows  between  the 
fibers.  They  are  numerous  in  young  teeth  and 


1 64       NORMAL   HISTOLOGY    AND    ORGANOGRAPHY. 

the  root.  They  produce  the  cementum  and  there- 
fore resemble  the  osteoblasts  of  bone.  They  have  a 
single  deep-staining  nucleus  and  irregular  processes 
that  fit  around  and  between  the  fibers  and  also  ex- 
tend into  the  cementum.  A  cementoblast  may  be- 
come enclosed  in  the  cementum  and  thus  form  a 
lacuna  which  it  completely  fills,  thus  making  a 


Fibro- 
blast. 


Dent  in. 


Fig.  119. —  Peridental  membrane  next  to  the  cementum  highly  mag- 
nified (Noyes). 

relatively  few  in  old  teeth.  The  single  nucleus  stains 
deeply,  being  rich  in  chromatin.  The  cells  are  small 
and,  as  their  name  implies,  their  function  is  the  pro- 
duction of  fibers  that  give  support  to  the  tooth. 

2.  The  cementoblasts  are  flat  irregular  cells  that 
fit  in  and  adjust  themselves  between  the  fibers  so  as 
to  form  a  single  layer  everywhere  over  the  surface  of 


DIGESTIVE  SYSTEM.  165 

cement  corpuscle  analogous  to  a  bone  corpuscle. 
Such  an  inclusion  is  the  exception  in  the  life  history 
of  these  cells. 

3.  The  osteoblasts  are  also  connective-tissue  cells, 
but  cover  the  bony  wall  of  the  alveoli.     They  lie 
between  the  fibers  and  their  function  is  the  pro- 
duction of  bone  which  anchors  the  supporting  fibers 
to  the  alveolar  wall.     These  cells  are  analogous  to 
the  osteoblasts  of  bone. 

4.  The    osteoclasts    are    large,    bone-destroying, 
multinucleated  cells  that  are  often  called  giant  cells. 
They  may  also  act  upon  and  absorb  the  cementum 
and  dentin.     They  are  not  constantly  present  in  the 
peridental   membrane   but    appear   whenever    cal- 
cified tissue  is  to  be  destroyed.     They  apply  them- 
selves to  the  surface  to  be  absorbed  and  by  their 
physiological  action  excavate  cavities  in  which  they 
lie,  known  as    Howship's  lacunce.     The  latter  may 
later  fill  in  with  new  cementum  or  bone,  thus  leaving 
a  permanent  record  of  the  process  of  absorption  and 
repair.     The  absorption  of  the  roots  of  deciduous 
teeth  results  from  the  physiological  action  of  the 
osteoclasts.     If  for  any  cause,  such  as  bacterial  in- 
vasion, the  osteoclasts   fail  to  appear,  the  root  of 
the  deciduous  tooth  does  not  absorb  but  remains  as 
a  permanent  obstruction  to  the  developing  new  tooth. 

5.  Epithelial  cells,  believed  by  some  to  be  remains 
of  the  enamel  organ,  envelop  the  surface  of  the  roots 
and  are  found  in  both  young  and  old  teeth.     Their 
function  is  not  known.     They  appear  as  cords  of 
epithelial  cells  that  anastomose  freely  to  form  an  en- 
veloping network,  which  nowhere  seems   to   unite 


1 66       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


with  the  epithelium  of  the  mucous  membrane  of  the 
mouth.  The  structure  of  some  of  these  cords  re- 
sembles that  of  tubular  glands,  and  Dr.  Black  has 
suggested  that  their  function  may  be  a  glandular  one. 
They  not  infrequently  enter  into  the  pathological 
conditions  of  the  peridental  membrane. 

Blood  Supply. — Usually  several  small  blood-vessels 
enter  the  foramina  at  the 
apex  of  the  root  and  pass  di- 
rectly to  the  pulp.  Upon 
reaching  the  pulp  these  ves- 
sels anastomose  freely,  form- 
ing an  extensive  blood  plexus. 
A  capillary  plexus  with  nar- 
row meshes  has  been  de- 
scribed between  the  layer  of 
odontoblasts  and  the  dentin, 
but  does  not  penetrate  the 
\l  *  latter.  Both  arteries  and 

lj J  veins  have  very  thin  walls 

and  may  be  easily  ruptured. 
The  pulp  therefore  bleeds 
very  easily  when  exposed. 
No  accompanying  lymphatics 
have  been  described. 

The  peridental  membrane, 

being  a  connective-tissue  layer,  has  a  very  rich  blood 
supply.  Vessels  enter  the  membrane  near  the  apex 
of  the  root,  accompanying  the  nerve  at  that  place; 
small  arterioles  penetrate  laterally  from  the  Haver- 
sian  canals  of  the  alveolar  wall,  and  a  third  supply 
is  derived  from  the  mucous  membrane  of  the  gum, 


Fig.  1 20. —  Showing  the  ar- 
rangement of  epithelial  cords 
or  glands  of  the  peridental 
membrane  around  the  root 
of  a  central  incisor  (dia- 
gram by  Dr.  Black). 


DIGESTIVE   SYSTEM. 


167 


vessels  passing  over  the  border  of  the  alveolar  proc- 
esses. This  vascular  condition  is  import  ant,  both  in 
health  and  disease. 

Nerve  Supply. — The  tooth  pulp  is  supplied  with 
nerve  fibers  from  the  fifth  cranial  nerve.  Medul- 
lated  dendrites  of  sensory  neurons  enter  the  pulp 
cavity  through  the  apical  foramen  of  the  root.  All 
of  them  lose  the  medullary  sheath,  but  do  so  at 
variable  distances  in  the  pulp.  The  varicose  den- 


Odontoblasts. 


1  Odonto- 
blasts. 


Terminal 
nerve  fiber. 


Fig.  121. —  Nerve  termination  in  the  pulp  of  a  rabbit's  molar, 
stained  in  methylene-blue  (intra  vitam):  a,  Odontoblasts  seen  in  side 
view;  b,  a  number  of  odontoblasts  seen  in  end  view,  showing  a  termi- 
nal branch  of  a  nerve  fiber  situated  between  the  odontoblasts  and  the 
dentin  (Huber). 


drites  ultimately  form  a  loose  plexus  immediately 
under  the  layer  of  odontoblasts  and,  therefore, 
practically  at  the  periphery  of  the  pulp.  Small 
branches  pass  from  this  plexus  to  terminate  between 
the  odontoblast  cells,  or  pass  through  the  layer  of 
odontoblasts,  but  in  no  case  have  they  been  traced 
into  the  dentin.  The  sensitive  dentin  is,  therefore, 
due  to  an  indirect  irritation  of  these  nerve  endings, 
conveyed  to  the  latter  through  the  medium  of  the 


1 68      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

dentinal  fibrils  and  the  odontoblasts.  The  pulp  is 
very  sensitive  to  traumatic  and  chemical  irritations, 
even  when  conveyed  to  it  through  the  constituents 
of  the  dentin.  It  is  especially  sensitive  to  changes  in 
temperature,  heat  or  cold  acting  alike.  It  has  no 
localized  sensation  of  touch. 

Our  knowledge  of  the  nerve  supply  of  the  periden- 
tal  membrane  is  not  extensive.  Both  medullated 
and  non-medullated  fibers  are  present,  the  latter 
being  a  part  of  the  sympathetic  nervous  system,  and 
accompany  as  well  as  innervate  the  small  blood- 
vessels. The  nerve  fibers  enter  the  peridental  mem- 
brane in  the  same  manner  and  from  the  same  sources 
as  the  blood  supply,  which  has  already  been  de- 
scribed. 

Attachment  of  Teeth. — In  considering  the  attach- 
ment of  teeth  it  must  be  remembered  that  teeth  are 
not  a  part  of  the  osseous  system  but  are  dermal 
appendages.  The  phylogenetic  history  of  this  sub- 
ject in  vertebrates  is  very  interesting.  The  de- 
scriptive literature  is  extensive  and  many  classifi- 
cations of  the  different  forms  of  attachment  have 
been  made.  Tomes,  in  his  "  Dental  Anatomy/' 
classifies  four  forms  of  attachment:  (i)  by  a  fibrous 
membrane;  (2)  hinge-joint;  (3)  ankylosis;  (4)  in- 
sertion in  a  socket. 

The  attachment  by  fibrous  tissue  is  manifest  in 
the  scaly  teeth  of  sharks.  Each  cone-shaped  tooth 
has  a  flattened  dermal  plate.  Calcified  connective 
tissue  is  built  into  this  plate,  which  it  unites  more  or 
less  fibrously  to  the  submucous  matrix  of  the  mouth. 
Such  teeth  are  practically  dermal  scales  and  have  no 


DIGESTIVE)   SYSTEM. 


169 


direct  attachment  to  the  bony  skeleton.  The 
hinge-joint  is  merely  a  modification  of  the  fibrous 
attachment,  and  is  found  in  many  fishes,  reaching  a 
high  degree  of  development  in  the  poison  fangs  of 
snakes.  The  hinge  is  composed  of  connective-tissue 
elements.  In  snakes  the  fang  has  a  muscular  at- 
tachment by  which  the  reptile  is  able  to  erect  the 
fang.  .By  ankylosis  is  meant  a  direct  calcified  union 
with  the  bone  of  the  jaw.  Such  teeth  have  no 
flattened  base,  but  a  calcified  pulp  which  binds  them 
firmly  to  the  bony 
skeleton  of  the 
mouth.  Ankylosis 
is  confined  to  the 
teeth  of  certain 
fishes. 

The  development 
of  a  socket  is  associ- 
ated with  large  teeth 
and  a  consequent 
strong  attachment . 
The  evolution  of  a 

socket  is  well  represented  phylogenetically  in 
reptiles  where  Wiedersheim  makes  three  classes: 
(i)  pleurodont  dentition  (lacertilia) ,  where  "the 
teeth  are  situated  upon  a  ledge  on  the  inner  side 
of  the  lower  jaw,  with  which  they  become  fused 
basally;"  (2)  acrodont  dentition  (chameleon,)  where 
"they  lie  on  the  free  upper  border  of  the  jaw;" 
(3)  thecodont  dentition  (crocodiles),  where  "'they  are 
lodged  in  alveoli."  In  man  all  the  teeth  are  im- 
bedded in  well-developed  alveoli  of  the  jaw-bones. 


Fig.  122. —  Diagram  illustrating  the  de- 
velopment of  a  socket,  a,  Pleurodont 
dentition;  &,  acrodont  dentition;  ct  the- 
codont dentition. 


170      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

Here  the  function  of  the  teeth  is  not  only  to  seize 
and  bite  the  food,  but  also  to  masticate  it  and  test 
its  quality.  This  change  in  function  accounts  for 
the  heterodont  dentition,  which  must  have  arisen  by 
a  modification  of  the  simple  homodont  condition 
in  which  the  teeth  are  all  small,  conical,  and  of  the 
same  size  and  shape.  The  primary  arrangement  of 
the  teeth  is  such  that  those  of  one  jaw  do  not 
usually  correspond  in  position  with  those  of  the 
other,  but  rather  with  the  interspaces  between  them. 
As  a  rule,  the  succession  of  teeth  in  man  is  nearly 
always  reduced  to  two  functional  sets,  the  deciduous 


Dental  ridge.  Enamel  organs.       Dental  ridge.     Enamel  organs.     Neck.    Dental 

ridge. 

Fig.  123. — Diagram  illustrating  the  development  of  the  enamel  organ 
of  three  teeth. 

teeth  and  the  permanent  teeth.  Traces  of  an 
earlier  set  have  been  found,  which  may  be  spoken  of 
as  a  "predeciduous"  dentition,  and  occasionally  one 
or  more  teeth  appear  which  replace  corresponding 
permanent  teeth,  and  thus  indicate  the  possibility  of 
an  extra  unrecorded  set.  An  unlimited  succession 
of  teeth  takes  place  in  nearly  all  vertebrates,  except 
with  mammals. 

Development  of  Teeth. — The  enamel  of  the  tooth 
develops  from  the  epithelium  of  the  oral  cavity.  In 
the  seventh  week  of  fetal  life  the  mucous  epithelium 
covering  the  gums  invaginates  to  form  a  dental 
groove.  The  ridge  or  shelf  thus  invaginated  is  called 


DIGESTIVE  SYSTEM. 


171 


Epithelium. 


the  dental  ridge.  Early  in  the  third  month  this 
dental  ridge  pro- 
duces lateral  proc- 
esses along  its  lin- 
gual side,  one  for 
each  deciduous 
tooth.  These  epi- 
thelial processes  or 
sacs  are  known  as 
enamel  organs  and 
develop  directly  into 
the  tooth  enamel. 
A  little  later,  during 
the  third  month,  a 
second  set  of  proc- 
esses comes  from  the 
lingual  side  of  the 
dental  ridge  and  in 
like  manner  forms 
the  enamel  organs  of 
the  permanent  set  of 
teeth. 

The  origin  of  the 
dentin  is  closely 
associated  with  the 
enamel  organs  but 
comes  from  the  con- 
nective tissue  under- 
lying these  organs. 
This  connective  tis- 
sue forms  dental 


Germ   for   per- 
manent  tooth. 

Enamel. 
Enamel  cells. 
Dentin. 

Odontoblasts. 


Pulp. 


Fig.   124. —  Diagram  illustrating   the  de- 
velopment of  a  tooth. 


172       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

papilla,  which  later  become  differentiated  into  the 
dentin  and  dental  pulp.  The  developing  papillae 
gradually  become  invested  by  the  enamel  organ  and 
one  by  one  erupt  on  the  surface  of  the  oral  cavity 
either  as  deciduous  or  permanent  teeth. 

It  will  be  observed  that  the  enamel  organs  are  sac- 
like  structures  consisting  of  an  outer  and  inner  layer 
of  epithelial  cells.  The  inner  layer  envelops  the 
dental  papillae  and  is  destined  to  form  the  enamel 
prisms.  The  outer  layer  becomes  associated  with  an 
investing  sheath  of  connective  tissue,  the  dental  sac, 
and  serves  as  a  temporary  protection  while  the 
enamel  is  being  formed.  When  the  tooth  erupts  the 
outer  lining  of  epithelial  cells  disappears. 

The  tooth  papillae  are  thus  all  preformed  at  the 
time  of  birth.  They  remain  latent  and  develop 
regularly  into  the  different  teeth  according  to  the 
table  on  page  144.  A  serious  illness  of  a  child  just 
before  their  eruption  may  affect  their  healthy 
growth  by  interfering  with  proper  nutrition,  and 
imperfect  and  pitted  teeth  result,  which  often  ac- 
counts for  an  early  decay. 

THE  TONGUE* 

The  tongue  is  a  voluntary  muscular  organ  that 
occupies  the  floor  of  the  mouth.  In  lower  verte- 
brates the  tongue  is  a  prehensile  organ.  In  many 
fishes  it  is  covered  with  teeth,  its  function  being  to 
capture  and  hold  prey.  In  frogs  and  toads  it  is 
covered  with  mucous  and  peculiarly  modified  to 
capture  insects.  In  reptiles  it  is  often  bifurcated, 
very  motile,  and  used  to  frighten  an  enemy.  In 


DIGESTIVE   SYSTEM. 


173 


woodpeckers  it  is  barbed  and  clearly  a  prehensile 
organ.     In  man,  while  the  organ  assists  in  taking 


Fig.  125. —  Papillar  surfaces  of  the  tongue,  with  the  fauces  and 
tonsils:  i,  i,  circumvallate  papillae,  in  front  of  2,  the  foramen  cecum; 
3,  fungiform  papillae;  4,  filiform  and  conical  papillae;  5,  transverse 
and  oblique  rugae;  6,  mucous  glands  at  the  base  of  the  tongue  and  in 
the  fauces;  7,  tonsils;  8,  part  of  the  epiglottis;  9,  median  glosso-epi- 
glottidean  fold  (fraenum  epiglottidis)  (from  Sappey). 

food,  its  more  important  function  is  gustatory,  the 
taste  organs  being  located  upon  its  surface.     For 


174       NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

description  the  tongue  may  be  divided  into  body, 
base,  inferior  surface,  and  dorsum. 

Body.— This  is  chiefly  made  up  of  striped  muscle 
which  may  be  divided  into  intrinsic  and  extrinsic. 
A  median  septum  divides  it  into  two  symmetrical 
lateral  halves.  Connective-tissue  elements,  nerves, 
the  body  of  glands,  and  blood-vessels  interlace 
freely  with  the  muscle.  The  musculature  is  best 
studied  in  a  beef's  tongue  that  has  been  boiled,  and 
is  a  subject  that  belongs  to  gross  anatomy.  In  any 
section  of  the  tongue,  muscle  fibers  will  be  seen  both 
in  cross  section  and  in  longitudinal  section. 

Base. — This  is  the  posterior  wide  end  of  the  tongue 
that  is  attached  to  the  hyoid  bone.  It  is  covered 
with  a  smooth  mucous  membrane,  beneath  which  is 
a  rich  supply  of  lymphoid  tissue.  The  latter  con- 
stitutes the  lingual  tonsil.  Mucous  glands  are  abun- 
dant. 

Inferior  Surface. — This  is  covered  with  smooth 
mucous  membrane  on  which  open  many  mucous  and 
serous  glands.  The  surface  is  divided  into  two 
halves  by  a  fibrous  septum  which  passes  to  the  floor 
of  the  mouth  and  is  known  as  the  lingual  frenum. 
When  this  is  abnormally  short  the  person  is  said  to  be 
tongue-tied,  and  speech  is  impaired. 

The  Dorsum. — This  surface  is  convex  both  from 
before  backward  and  from  side  to  side.  A  median 
depression,  or  sulcus,  divides  it  into  lateral  halves. 
The  sulcus  apex  points  backward  to  the  foramen 
cecum  just  in  front  of  the  base.  This  cecum  is  a 
blind  pocket  that  marks  the  origin  of  the  middle 
portion  of  the  thyroid  gland,  and  is  the  remnant  of 


DIGESTIVE   SYSTEM. 


175 


the  obliterated  thyroid  duct.  The  dorsal  surface  is 
studded  with  three  sets  of  papillae,  to  be  described  in 
detail. 

Papillae. — i.  Filiform  Papillae. — These  are  not 
only  the  smallest  but  by  far  the  most  numerous,  and 
give  the  tongue  a  velvety  appearance.  They  are 
arranged  in  divergent  rows  that  extend  outward  and 
forward  from  the  median  sulcus.  Each  papilla  is 
conical,  points  backward,  and  is  covered  by  a  thick 


Fig.  126. — Section  through  two  filiform  papillae  of  tongue. 

layer  of  stratified,  horny,  squamous  epithelium. 
The  function  of  these  papillae  is  purely  prehensile. 
In  carnivorous  animals  they  give  the  tongue  a  rasp- 
like  structure  that  serves  effectually  in  cleaning 
bones.  It  is  said  that  a  tiger,  in  this  way,  can  draw 
blood  from  a  living  hand. 

2.  Fungiform  Papilla. — These  are  less  numerous, 
larger,  and  supplied  with  blood,  which  gives  them  a 


176      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

red  color.  They  are  most  numerous  at  the  tip  and 
margins  of  the  tongue.  Each  is  like  an  inverted 
cone  and  has  a  covering  of  eight  or  ten  layers  of 
squamous  epithelial  cells.  Many  of  these  papillae 
have  taste  buds  in  their  lateral  walls,  analogous  to 
those  to  be  described  in  the  third  class  of  papillae— 
the  circumvallate.  A  connective-tissue  papilla  oc- 
cupies the  core  of  the  fungiform.  This  core  has  a 
rich  supply  of  blood-vessels  which  in  fevers  become 
congested  with  blood  and  give  the  dorsum  a 


Fig.  127. — Section  of  fungiform  papilla  of  tongue. 

speckled  red  color,  spoken  of  as  strawberry  tongue 
This  is  particularly  the  case  in  scarlet  fever. 

3.  Circumvallate  Papilla. — These  are  by  far  th 
largest  and  are  found  just  in  front  of  the  foramen 
cecum.     They  are  about  ten  in  number  and  are  ar- 
ranged in  the  form  of  a  letter  V,  with  the  apex  point- 
ing backward.     They  resemble  the  fungiform  pa 
pillae,  only  they  are  much  larger.     Each  papilla  is 
surrounded  by  a  deep,  narrow,  circular  trench  or 


DIGESTIVE  SYSTEM. 


177 


fossa,  hence  their  name.  The  wall  consists  of  strati- 
fied squamous  epithelium  and  the  core  of  connective 
tissue  richly  supplied  with  blood-vessels.  From  this 
core  secondary  connective-tissue  papillae  indent  the 
under  surface  of  the  stratified  epithelial  wall. 

Taste  Buds. — These  are  nests  of  epithelial  cells 
that  lie  in  the  lateral  walls  of  circumvallate  and 


Epithe- 
lium. 


pbner's 

gland. 


Fig.  128.  —  Longitudinal  section  of  a  human  circumvallate  papilla 
(Bohm  and  Davidoff). 


fungiform  papillae,  and  are  closely  associated 
with  the  sense  of  taste.  They  resemble  small  acorns, 
and  are  made  up  of  columnar  cells  so  arranged  as  to 
form  a  central  taste  canal,  which  in  turn  opens  by  a 
pore  into  the  circumvallate  fossa.  Two  kinds  of 
slender  epithelial  cells  are  present,  (i)  tegmental  or 


?J&      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

cover  cells,  principally  at  the  periphery  of  the  bud, 
which  support  or  ensheath  (2)  the  gustatory  or  taste 
cells.  The  latter  are  smaller,  more  delicate  and 
centrally  placed,  with  the  distal  or  free  end  bearing 
a  small  process  that  projects  into  the  inner  taste  pore. 
The  cells  of  the  taste  bud  occupy  the  whole  lateral 
wall ;  that  is,  the  base  of  each  cell  rests  upon  the  base- 
ment membrane  next  to  the  connective-tissue  core 
and  the  distal  end  extends  practically  to  the  sulcus 


"x.-.i^r-     -  .y_.-  — 


Taste  buds. 


Fig.  129.  —  Two  foliate  papillae  from  tongue  of  rabbit. 

of  the  papilla.  These  taste  buds,  as  a  matter  of  pro- 
tection, develop  in  the  lateral  wall  rather  than  in  the 
exposed  dorsal  surface  of  each  papilla. 

The  nerve  fibers  of  the  gustatory  nerve  are  not  in 
protoplasmic  continuity  with  the  epithelial  cells  of 
the  taste  buds,  as  is  the  case  with  the  sensory  cells  of 
the  olfactory  region.  Nerve  fibers  enter  the  taste 
buds  and  terminate  in  varicosities  that  interlace 
and  come  in  contact  with  the  gustatory  cells  of  each 


DIGESTIVE   SYSTEM. 


179 


taste  bud.  It  is  evident  that  a  food  to  be  tasted 
must  first  be  put  into  solution  to  pass  into  the  sulcus 
and  stimulate  the  delicate  processes  of  the  gustatory 
cells  of  taste  buds. 

Foliate  Papillae. — On  each  side  of  the  rabbit's 
tongue,  some  distance  back,  can  be  seen  a  small  oval 
patch,  with  diagonal  grooves  and  ridges,  resembling 
the  side  of  a  three-cornered  file.  These  patches  are 
the  foliate  papilla.  In  reality  they  are  not  papillae 
but  alternating  grooves  and  ridges.  In  transverse 
section,  the  lateral  walls  of  the  ridges  will  be  found 
beset  with  taste  buds  resembling  in  detail  those 


-  Surface 
pore. 


Fig.    130. — Section     through 
taste  bud. 


Fig.  131. — Cells  from  a  taste 
bud:  a,  taste  cells;  b,  supporting 
cells. 


described  in  the  circumvallate  papillae.  The  rabbit, 
therefore,  to  relish  his  clover,  should  roll  the  leaves 
over  these  lateral  patches. 

Glands  of  the  Tongue. — Small  serous  racemose 
glands  are  associated  with  the  circumvallate  pa- 
pillae into  the  fossa  of  which  their  ducts  open. 
Glands  are  otherwise  absent  over  the  dorsum  of  the 
tongue.  Over  the  other  parts  of  the  tongue  both 
serous  and  mucous  glands  are  abundantly  present. 
Many  of  these  are  mixed  serous  and  mucous  glands. 


180       NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

Blood  Supply. — The  arteries  are  the  lingual, 
which  branches  to  form  (i)  the  dorsal  lingual  artery 
which  anastomoses  freely  with  the  tonsillar  branch 
of  the  facial,  and  (2)  the  ranine  artery  that  passes 
along  the  under  surface.  The  veins  are  the  ranine 
and  the  dor  sails  lingua  that  drain  into  the  internal 
jugular. 

Nerves. — These  are  (i)  the  hypoglossal,  the  motor 
nerve;  (2)  the  lingual,  from  the  inferior  maxillary 
of  the  fifth,  which  is  accompanied  by  the  chorda 
tympani  of  the  seventh,  or  facial;  (3)  the  glosso- 
pharyngeal,  which  supplies  the  taste  buds;  (4)  the 
internal  laryngeal.  Many  fibers  of  the  sympathetic 
system  mingle  with  these  nerves. 

PHARYNX. 

The  pharynx  is  the  common  passage  for  both 
food  and  air.  It  is  an  expanded  portion  of  the  di- 
gestive tube  five  inches  in  length  and  with  seven 
openings:  one,  the  fauces  from  the  mouth;  two 
posterior  nares;  two  Eustachian  tubes;  one  to  the 
trachea,  and  the  orifice  of  the  esophagus. 

The  mucous  membrane  of  the  pharynx  is  lined 
with  stratified  squamous  epithelium,  except  in  the 
region  of  the  posterior  nares  where  the  epithelium 
is  ciliated.  In  the  submucosa  there  is  a  generous 
supply  of  mucous  and  serous  glands  and  lymphoid 
tissue.  The  latter  is  particularly  abundant  in  the 
region  of  the  posterior  nares,  forming  in  this  location 
the  pharyngeal  tonsils  or  adenoids.  In  early  youth 
the  adenoids  are  prone  to  enlarge  so  as  to  obstruct 
normal  breathing,  a  condition  that  justifies  their 
removal.  A  rich  supply  of  elastic  longitudinal 


DIGESTIVE  SYSTEM. 


181 


connective-tissue  fibers  is  also  present  in  the  sub- 
mucosa.  The  submucosa  is  therefore  capable  of 
being  greatly  distended,  as  is  the  case  in  throat  in- 
fections, such  as  diphtheria,  where  the  congestion 
is  so  great  as  to  interfere  with  respiration.  The 
diphtheria  germs  and  toxins  are  thus  lifted  up  and 
walled  off  from  the  deeper  structures  and  normal 


KL-  Epithelium. 


Striated  muscle. 


Crypt. 

Lymph  oid  nodules. 


Tonsillar  sinus. 


Fig.  132. — Section  through  the  pharyngeal  tonsil  of  man  (Sobotta). 

blood  supply.  This  is  nature's  method  of  eliminat- 
ing the  disease,  with  the  possible  danger  to  the  pa- 
tient of  suffocation. 

External  to  the  submucosa  come  several  layers  of 
striated  muscle  fibers  forming  the  pharyngeal  muscle, 
the  description  of  which  belongs  to  gross  anatomy. 

Tonsil. — The  tonsils  are  two  oval  lymphoid 
masses  imbedded  in  the  lateral  walls  of  the  pharynx, 


1 82      NORMAL    HISTOLOGY    AND    ORGANOGRAPHY. 


opposite  the  root  of  the  tongue  and  between  the 
anterior  and  posterior  palatine  arches.  This  lymph- 
oid  tissue  is  covered  with  the  oral  mucous  mem- 
brane, beset  with  many  depressions  or  pits  known 
as  crypts.  It  is  along  these  crypts  that  bacteria 
may  enter  the  tonsil,  producing  an  inflammation  of 
that  organ  known  as  tonsillitis. 


Stratified  epithelium. 


Muscularis  mucosa. 


Mucous  glands  in  the 
submucosa. 


Circular  muscle  layer. 


Longitudinal  muscle 
layer. 


Fibrous  coat. 
Fig-  I33- — Cross  section  of  the  esophagus. 

ESOPHAGUS. 

The  esophagus  is  the  part  of  the  alimentary  canal 
that  intervenes  between  the  pharynx  and  the  stom- 
ach, and  is  a  very  muscular  tube  about  ten  inches 
in  length.  Its  upper  end  is  opposite  the  lower  bor- 
der of  the  crycoid  cartilage  and  the  sixth  cervical 
vertebra.  The  lower  end  or  cardiac  orifice  is  oppo- 


DIGESTIVE  SYSTEM.  jg-j 

site  the  eleventh  dorsal  vertebra.  Two  distinct 
constrictions  are  present,  one  at  the  beginning  and 
one  where  it  is  crossed  by  the  left  bronchus.  The 
normal  distention  at  these  points  is  about  four- 
fifths  inch. 

The  wall  of  the  esophagus  may  be  divided  into 
four  coats:  mucous,  submucous,  muscular,  and 
fibrous. 

1.  Mucous    Layer. — This    layer    is    thrown    into 
many  longitudinal  folds  and  lined,  as  in  the  pharynx, 
with  stratified  epithelium.     The  tunica  propria  is 
well   developed   and   may   contain   solitary  lymph 
nodes.     Tubular   glands   resembling   those   of   the 
stomach  are  found  in  patches,  particularly  at  the 
extremities  of  the  esophagus.     They  are  entirely 
confined  to  the  mucosa  and  distinct  from  the  mucous 
glands  found  in  the  submucosa.     Their  function  is 
problematic.     A  muscular  is  mucosa  is  present  in  the 
esophagus  just  external  to  the  tunica  propria,  con- 
sisting  of   longitudinally   disposed   smooth   muscle 
cells.     This  layer  becomes  more  prominent  in  the 
alimentary  canal  below  the  esophagus. 

2.  Submucosa. — This  layer  lies  just  external  to 
the  muscularis  mucosa  and  consists  of  loose  con- 
nective-tissue elements,  blood  and  lymph  vessels, 
nerves  and  the  bodies  of  mucous  glands.     These 
glands  are  compound  racemose  and  are  particularly 
abundant  in  the  lower  part  of  the  esophagus.     The 
ducts  pass  through  the  muscular  mucosa  to  open  on 
the  epithelial  surface.     They  secrete  mucus  for  the 
lubrication  and  protection  of  this  surface.     Not  in- 
frequently the  morning  vomit  of  mucus  in  chronic 


1 84      NORMAIv   HISTOLOGY   AND   ORGANOGRAPHY. 

gastritis  comes  from  excessive  secretion  of  these 
glands.  The  tissues  of  the  submucosa  are  loosely 
held  together,  and  sections,  therefore,  may  tear  along 
this  layer. 

3.  Muscular  Coat. — This  consists  of  an  inner  cir- 
cular and  an  outer  longitudinal  layer,  although  the 
fibers    of    each   often   interlace.     The    longitudinal 
layer  is  particularly  strong,  often  thicker  than  the 
circular.     In  the  upper  half  many  striated  fibers  are 
present  that  are  continuous  with  the  pharyngeal 
voluntary  muscle.     The  control  of  these  fibers  en- 
ables the  dog  to  return  food  to  the  mouth  that  has 
passed  into  the  upper  part  of  the  esophagus.  '  In  the 
lower  half,  only  smooth  muscle  fibers  are  present. 
The  longitudinal  layer  passes  on  as  the  longitudinal 
layer  of  the  stomach  and  intestine,  while  the  circular 
becomes  the  diagonal  fibers  of  the  stomach  and  does 
not  pass  to  the  intestine.     Connective- tissue  ele- 
ments interlace  and  strengthen  the  whole  muscu- 
lature.    Foods  and  liquids  are  carried  along  this 
tube  by  peristaltic  contraction  of  its  muscles,  and 
in  this  way  cattle  and  horses  can  take  nourishment 
without  lifting  their  heads. 

4.  Fibrous  Coat. — This  consists  of  loose  connec- 
tive-tissue elements,  mostly  white  fibrous,  binding 
the   esophagus   to   adjacent   structures.     It   is   not 
well  defined  and  often  difficult  to  demonstrate  as  a 
distinct  layer. 

STOMACH. 

The  stomach  varies  greatly  in  form  and  position 
according  to  physiological  conditions.  For  de- 
scriptive purposes  it  has  two  ends,  cardiac  and  py- 


DIGESTIVE  SYSTEM.  185 

loric;  two  surfaces,  dorsal  and  ventral;  two  curva- 
tures, greater  and  lesser;  and  two  orifices,  esophageal 
and  pyloric.  The  most  fixed  point  is  the  esophageal 
orifice,  which  is  situated  opposite  the  seventh  left 
costal  cartilage  one  inch  from  the  sternal  junction. 
The  most  movable  portion  is  the  pyloric  end,  which 
is  situated  one-half  to  one  and  one-half  inches  to  the 
right  of  a  median  plane  and  a  variable  distance  be- 
low the  esophageal  opening.  The  distance  between 


Fig.  134. — Anterior  outlines  of  stomach.     (His'  model.) 

the  two  orifices  is  about  four  inches.  The  full 
length  of  the  stomach  is  about  ten  inches,  and  the 
greatest  diameter  four  inches,  with  average  capacity 
of  one  quart.  These  dimensions  are  subject  to 
great  variations, 

The  stomach  wall,  like  that  of  other  parts  of  the 
food  canal,  is  made  up  of  four  layers :  mucosa,  submu- 
cosa,  muscularis,  and  serosa. 

I.  Mucosa. — The  mucous  surface  is  uneven,  due 


1 86     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


to  irregular  folds.  The  surface  is  beset  with  minute 
pores  or  circular  depressions,  called  crypts,  into 
which  the  gastric  glands  open.  As  in  other  parts 
of  the  food  canal  this  layer  consists  of  epithelium, 
membrana  propria,  and  muscularis  mucosa.  The 
epithelium  is  simple  columnar  with  the  nucleus  near 
the  bottom  of  the  cell,  leaving  a  clear  proximal  half 


Crypt. 


Gastric  glands. 


Muscularis  mucosa. 


" —  Submucosa. 


Circular  muscle  layer. 


Longitudinal  muscle 

layer. 
Serous  coat. 

Fig.  135. — Cross  section  through  the  wall  of  a  stomach. 

to  each  cell  that  does  not  readily  stain.  The  pits  or 
crypts  are  lined  by  this  same  epithelium.  The 
membrana  propria  has  a  rich  supply  of  connective- 
tissue  cells  and  extensive  ramifications  of  blood  and 
lymph  capillaries.  The  muscularis  mucosa  is  a  thin 
muscle  layer,  external  to  the  membrana  propria, 
and  consists  of  an  inner  layer  of  circular  and  an  outer 


DIGESTIVE   SYSTEM. 


i87 


Crypt. 


Parietal  cell. 


layer  of  longitudinal  smooth  muscle  fibers.  A  liberal 
supply  of  connective  tissue  is  associated  with  this 
muscle.  This  layer,  therefore,  offers  resistance  to 
an  invasion  of  bacteria,  while  the  muscular  contrac- 
tion relieves  pressure  to  the  rich  blood  supply  in  the 
submucosa  just  external  to  it,  and  at  the  same  time 
exerts  pressure  upon  the  gastric  glands. 

Gastric  Glands.— 
These  are  widely  dis- 
tributed and  per- 
haps the  most  impor- 
tant structures  of 
the  mucosa.  They 
are  simple  tubular, 
except  in  the  pyloric 
region,  where  many 
of  them  are 
branched.  Usually 
several  glands  open 
into  each  crypt,  the 
latter  representing 
a  circular  pit-like 
evagination  of  the 
epithelial  surface . 
The  wall  of  each 
gland  consists  of 
simple  epithelium  and  two  kinds  of  cells  are  present : 
(i)  chief  cells,  which  are  by  far  the  most  numerous; 
these  are  round  or  cuboid  cells,  with  central  nucleus 
that  stains  blue  with  hematoxylin ;  (2)  parietal  cells , 
which  are  less  numerous,  larger,  and  have  a  granular 
cytoplasm  that  takes  the  red  eosin  stain.  They  inter- 


Chief  cell. 


Fig.  136. — Simple    tubular    gland    from 
stomach. 


1 88      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


vene  with  the  chief  cells  but  are  placed  at  the  pe- 
riphery of  the  glands,  and  communicate  with  the 
central  lumen  by  means  of  a  network  of  secreting 
ducts.  They  are  most  abundant  in  the  cardiac 
end  of  the  stomach  and  along  the 
•middle  and  inner  third  of  each 
gland.  These  cells  are  supposed  to 
have  something  to  do  with  the  se- 
cretion of  hydrochloric  acid.  The 
cytoplasm  of  the  chief  cells  contains 
granules  of  pepsinogen,  which  is 
converted  into  pepsin  of  the  gastric 
juice.  During  fasting,  these  gran- 
ules accumulate,  and  during,  or 
after,  active  secretion  they  become 
smaller  and  tend  to  disappear. 
The  mucosa  secretes  a  varying 
amount  of  mucus  for  the  protec- 
tion of  the  delicate  epithelial  sur- 
face .  In  many  forms  of  indigestion , 
and  particularly  in  poison  cases, 
the  mucus  secretion  is  very  exten- 
sive and  serves  to  keep  the  irrita- 
ting stomach  contents  away  from 
the  epithelial  lining.  The  excess 
of  mucus  can  be  removed  by  stom- 
ach lavage. 

The  chief  difference  between  the 
pyloric  and  cardiac  regions  of  the 
stomach  is  found  in  the  mucosa.  (i)  The  crypts  in 
the  cardiac  end  are  shallow,  while  in  the  pyloric  end 
the  crypts  frequently  extend  half  way  through  the 
thickness  of  the  mucosa.  (2)  The  gastric  glands 


Fig.  137. — A  num- 
ber of  fundus  glands 
from  the  fundus  of 
the  stomach  of  young 
dog,  stained  after 
the  chrome  -  silver 
method,  showing  the 
system  of  fine  canals 
surrounding  the  pa- 
rietal cells  and  com- 
municating with  the 
lumen  of  the  glands 
(Huber). 


DIGESTIVE  SYSTEM, 


189 


are  longer  than  the  crypts  in  the  cardiac  end; 
towards  the  pyloric  end  the  glands  become  shorter, 
tortuous,  and  pressed  closely  against  the  muscu- 
laris  mucosa.  Many  of  the  pyloric  glands  are 
branched.  (3)  The  parietal  cells  are  numerous  in 


Fig.  138. — From  a  section  through  the  junction  of  the  human  esophagus 
and  cardia  (Bohm  and  Davidoff). 

the  cardiac  region  and  practically  absent  in  the 
pyloric.  The  pyloric  mucosa,  in  this  way,  comes  to 
resemble  that  of  the  small  intestine.  In  addition 
an  occasional  villus  or  Brunner's  gland  may  be  found 
in  the  pyloric  end. 

2.  Submucosa. — The  submucosa  in  all  mucous 
membranes  is  highly  vascular.  Besides  blood  and 
lymph  there  is  an  abundant  supply  of  connective- 


1 90      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 


Epithelium 
of  fold  be- 
tween gas- 
tric crypt. 


Gastric 
crypt. 


tissue  elements,   largely  elastic  fibers,   connective- 
tissue  cells  and  fat  cells.     Nerve  cells  and  nerve 

fibers,  known  as 
Meisner's  plexus,  are 
found  here  and  in  the 
submucosa  through- 
out the  alimentary 
canal. 

3.  Muscular  is.— 
This  consists  of 
smooth  muscle  and 
may  be  divided  into 
three  layers  :  (a)  an 
inner  sheath  where 
the  fibers  run  ob- 
liquely; this  sheath 
is  continuous  with 
the  circular  layer  of 
the  esophagus;  (ft) 
a  middle  circular 
layer  which  is  con- 
tinued as  the  circu- 
lar layer  of  the  in- 
testine; (c)  an  outer 
longitudinal  layer 
continuous  with  the 


Fig     i39.—  From    vertical  section 


longitudinal  layer  of 
both  esophagus  and  intestine;  nerve  cells  and 
nerve  fibers  form  a  plexus  between  the  longitudinal 
and  circular  muscle  of  the  whole  alimentary  tract, 
which  is  known  as  the  plexus  of  Auerbach. 

4.  Serosa.  —  This  consists  of  a  thin  layer  of  fibrous 
tissue  covered  by  simple  pavement  epithelial  cells 


DIGESTIVE   SYSTEM. 


Chief  cell.  - — 
Lumen.  — 


Fig.  140. — Section  through  fundus  of  human  stomach  in  a  condition  of 
hunger  (Bohm  and  Davidoff) 


Lumen. 


L.   —  Mucosa. 


Parietal 

cell. 


Fig.  141.— Section  through  fundus  of  human  stomach  during  digestion 
(Bohm  and  Davidoff). 


1 92      NORMAL,   HISTOLOGY  AND    ORGANOGRAPHY. 


Papilla. 


Stratified  epi- 
thelium. 
Submucosa. 


musde. 


and  bound  down  to  the  muscularis  by  delicate 
fibrous  septa.  It  is  really  a  part  of  the  peritoneum. 
The  Stomach  in  Ruminants. — Ruminants  (ox, 
sheep,  goat,  camel,  llama)  all  have  four  compart- 
ments for  the  reception  and  maceration  of  food; 

rumen,  reticulum,  oma- 
sum, and  abomasum. 
The  first  three  are 
morphologically  dis- 
tensions and  modifica- 
tions of  the  lower  end 
of  the  esophagus,  while 
the  abomasum  alone 
corresponds  to  the 
stomach  in  other  ani- 
mals and  needs,  there- 
fore, no  further  de- 
scription here. 

The  Rumen  is  by  far 
the  largest  compart- 
ment, reaching  the 
serous  coat.  enormous  capacity  of 
forty  gallons  in  the  ox. 
It  is  divided  into  four 
sac-like  pouches  by 

two  muscular  band-like  girdles  whose  obvious  func- 
tion is  to  contract  on  the  contents  and  render 
assistance  in  the  mechanical  process  of  returning 
food  for  further  mastication.  Its  mucous  mem- 
brane is  covered  with  pointed  papillae  3  to  9  mm.  in 
length,  excepting  where  the  muscular  pillars  are 
most  prominent.  Its  epithelial  lining  is  stratified, 
consisting  of  eight  to  twelve  lavers  of  cells,  the 


Fig.  1410. — Cross    section  through 
rumen  of  ox. 


DIGESTIVE   SYSTEM.  193 

inner  ones  being  very  scaly  and  presenting  a  fibrous- 
like  structure.  The  submucosa  is  vascular,  with  a 
scattering  of  small  mucous  glands,  but  these  form 
no  digestive  secretion.  Strands  of  smooth  muscle 
fibers  extend  into  the  core  of  each  papilla  of  the 
mucosa,  also  a  net- work  of  blood  and  lymph  vessels. 
There  are  two  smooth  muscle  layers,  an  inner  cir- 
cular and  an  outer  longitudinal,  the  inner  layer 
being  much  the  heavier.  Like  the  esophagus, 
these  layers  show  a  fine  cross-striation,  and  there  is 
no  doubt  but  that  these  layers  assist  in  the  mechan- 
ical process  of  returning  the  food  to  the  mouth  for 
a  more  thorough  mastication.  The  serosa  is  unusually 
heavy  and  easily  detected  in  microscopic  sections. 

The  Reticulum  is  the  second  gastric  reservoir  and 
is  the  smallest  compartment.  Its  mucous  surface 
presents  a  honeycomb  appearance  when  seen  from 
the  inside,  hence  its  name.  The  muscular  tunic  is 
thin,  otherwise  the  other  layers  are  analogous  to 
those  found  in  the  rumen. 

The  Omasum,  or  third  compartment,  is  only  a 
little  larger  than  the  reticulum.  The  mucous  mem- 
brane is  extensively  folded  to  form  large  leaves  ex- 
tending the  length  of  the  organ.  Between  the 
large  leaves  are  smaller  leaves,  and  again  a  third 
and  a  fourth  series,  making  altogether  about  400 
laminae  of  variable  sizes.  These  leaves  bear  horny 
papillae,  being  large  and  pointed  toward  the  reticu- 
lum end  and  small  and  warty  toward  the  omasum 
end.  These  leaves  are  lined  with  eight  to  twelve 
layers  of  scaly,  tesselated  epithelial  cells,  forming  a 
rough  gritty  surface.  A  liberal  supply  of  smooth 
muscle  is  present  in  the  center  of  each  leaf,  also  a 


194     NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 


network  of  blood-  and  lymph- vessels.  The  physio- 
logical action  of  this  muscle  causes  adjacent  leaves 
to  rub  against  each  other,  producing  a  trituration  of 
the  retained  food.  The  muscular  coat  is  fasciculated 
and  thin  and  composed  of  two  layers  that  pass  in  dif- 
ferent directions.  The  serosa  presents  nothing  differ- 
ent from  the  general  structure  of  the  peritoneal  lining. 

SMALL  INTESTINE, 

The  small  intestine  is  about  twenty-four  feet  long, 
and  is  divided  into  duodenum,  ten  inches :  jejunum  and 


_    Villus. 


-  Crypt  of  Lieberkiihn. 
—  Muscularis  mucosa. 


r—  -   Circular  muscle  layer. 

Longitudinal  muscle 

layer. 
Serous  coat. 


Fig.  142. — Cross-section  of  small  intestine. 

ileum,  respectively,  two-fifths  and  three-fifths  of  the 
remainder.     About  three  feet  from  the  lower  end  of 


DIGESTIVE   SYSTEM. 


195 


Fig.  143. — Portion  of  the  wall  of 
the  small  intestine,  laid  open  to  show 
the  valvulae  conniventes  (Brinton). 


the  ileum  Meckel's  diverticulum  may  be  present,  rep- 
resenting the  last  embryonic  closure  of  the  intestine. 
The  intestine  has  the  same  number  of  layers  as  the 
stomach.  The  muscularis,  however,  consists  of  but 
two  strata,  an  inner  circular  and  an  outer  longitudinal, 
i.  Mucosa. — The  mucosa  is  lined  by  simple  co- 
lumnar epithelium  in 
which  many  goblet 
cells  are  present,  par- 
ticularly in  the  deeper 
folds.  Themembrana 
propria  and  muscu- 
laris mucosa  are  iden- 
tical with  those  des- 
cribed in  the  stomach. 
The  mucous  surface  of  the  small  intestine  is  much 
increased  by  means  of  folds,  of  which  there  are  three 

mechanisms: 
valvulcB  conni- 
ventes, villi,  and 
crypts  of  Lie- 
berkuhn. 

(a)  ValvulcB 
Conniventes.  — 
These  are  con- 
centric, trans- 
verse, crescen- 
tic  folds  of  the 
mucosa,  that 
usually  form 
two-thirds  of  a 
circle,  although  occasionally  one  forms  an  entire 
circle  or  even  a  spiral.  These  valves  are  two  or  three 


Fig.  144. — Mucous  membrane  of  the  jejunum, 
highly  magnified  (schematic):  i,  i,  Intestinal  villi; 
2,  2,  closed  or  solitary  follicles;  3,  3,  orifices  of 
the  follicles  of  Lieberkiihn  (Testut). 


196     NORMAL  HISTOLOGY   AND    ORGANOGRAPHY. 

inches  long,  about  one-third  inch  broad  and  one- 
eighth  inch  thick.  The  inner  surface  of  the  small  in- 
testine is  thus  thrown  up  in  a  series  of  shelves.  This 
mechanism  has  an  analogue  in  the  typhlosole  of  the 
earthworm  and  the  spiral  valve  of  some  fishes. 

(6)  Villi. — These  are  tongue-like  elevations  of  the 
mucosa  one-thirtieth  to  one-fortieth  inch  in  height, 
and  barely  visible  to  the  naked  eye.  They  are 
found  on  both  sides  of  the  valvulae  conniventes 
and  on  the  general  surface  of  the  mucosa.  Collec- 
tively they  give  the  surface  a  velvety  appearance. 
The  villi  are  most  numerous  in  the  upper  part  of  the 
intestine,  where  they  number  fifty  to  eighty  to  the 
square  inch.  They  are  longer  but  more  slender  and 
less  numerous  in  the  ileum,  where  they  number 
forty  to  sixty  to  the  square  inch.  Their  total  num- 


Fig.  145. — at  Cross  section  of  a  villus;    b,  cross  section  of  crypt  of  Lie- 
berkiihn. 

ber  in  the  small  intestine  is  estimated  at  4,000,000. 
Each  villus  has  a  lining  of  simple  columnar 
epithelium  which  covers  a  connective-tissue  core. 
A  few  smooth  muscle  fibers  enter  this  core  from 
the  muscularis  mucosa.  In  addition  there  is  a 
rich  blood  supply  and  a  central  lymphatic  duct. 
The  latter  is  a  part  of  the  lymphatic  system  of 
the  intestine  known  as  lacteals  because  of  the  milky 


SYSTEM. 


197 


lymph  they  contain  after  each  meal.  The  villi  de- 
velop as  invaginations  of  the  mucosa  and  are  exclu- 
sively confined  to  the  small  intestine. 

(c)  Crypts  of  Lieberkuhn. — These  are  sometimes 
spoken  of  as  intestinal  glands.  They  consist  of  pits 
or  evaginated  diverticulce  of  the  mucous  epithelium 
that  open  as  pores  between  the  bases  of  the  villi. 
The  bottom  of  these  crypts  rests  against  the  muscu- 
laris  mucosa.  Goblet  cells  are  particularly  numer- 
ous in  the  epithelial  lining  of  their  walls.  Crypts 


-Central 
chyle-vessel 
of  villas. 


.yle-vessel. 


Artery. 


-Mucosa. 
l-Muscularis 
mucosse. 
-Submucosa. 

Plexus  of 
'•    lymph-ves- 
sels. 

.    Circular  mus- 
~~    cular  layer. 

Plexus  of 
.,    lymph-ves- 
.%•%»       sels. 
.-.>":  V~.7"  Long,  muse. 

" —       layer  with 

serous  coat. 


Fig.  146. — Schematic  transverse  section  of  the  human  small  intestine 
(after  F.  P.  Mall). 

are  also  present  in  the  large  intestine  and  are  analo- 
gous to  the  shorter  crypts  of  the  stomach  into  which 
the  gastric  glands  open. 

Snlitarv  T.vm<hk  Nodules. — These  are  simple  nodes 


198      NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 


Villus. 


of  lymph  tissue  situated  just  beneath  the  mucous 
epithelium.  They  are  found  along  the  whole  ali- 
mentary tract  and  in  all  mucous  membranes. 

Peyer's  Patches,  or  Agminated  Lymph  Nodules. — 
These  appear  as  oval  elevations  on  the  mucous  sur- 
face and  are  collections  of  lymph  nodules.  They 
may  be  three  inches  long  or  less,  and  one-third  to 
one-half  inch  broad.  They  number  from  thirty  to 
forty,  and  are  found  in  the  ileum  and  always  in  the 

mucous  surface  op- 
posite the  mesen- 
teric  attachment, 
the  long  axis  being 
parallel  with  that 
of  the  intestine. 
Their  bodies  usu- 
ally extend  to  the 
circular  muscle 
layer  and  they 
therefore  invade 
the  submucosa. 
Villi  are  either 
stunted  or  altogeth- 
er absent  over  these 
patches.  In  early 
youth  they  are  very 
prominent,  while  in 
middle  life  they  be- 
gin to  atrophy,  and 
in  old  age  they  may  entirely  disappear. 

The  patches  are  the  seat  of  ulcerations,  particu- 
larly in  typhoid  fever  and  tuberculosis.  The  latter 
form  transverse  ulcers  as  the  bacteria  of  tuberculosis 


Fig.   147. — Longitudinal  section  of  ileum 
showing  part  of  a  Peyer's  patch. 


DIGESTIVE  SYSTEM. 


199 


Vittus. 


spread  along  the  lymphatics  which  are  here  trans- 
verse to  the  intestine.  The  typhoid  germ  produces 
an  ulcer  whose  long  axis  is  parallel  to  that  of  the 
intestine. 

Brunner's  Glands. — These  are  branched  tubular 
glands  whose  bodies  are  situated  in  the  submucosa 
and  whose  ducts 
pass  through  the 
muscularis  mucosa 
to  open  between  or 
into  the  crypts  of 
Lieberkuhn.  They 
are  confined  to  the 
duodenum,  partic- 
uarly  the  upper 
part.  Occasionally 
they  may  be  found 
in  the  pyloric  end 
of  the  stomach. 
The  cells  resemble 
those  of  the  pyloric 
glands,  being  cylin- 
drical and  finely 
granular.  B  run- 
ner's glands  are 
easily  recognized , 
as  they  are  the  only 
glands  that  lie  in 
the  submucosa. 

2.  Submucosa. — 


Longitudi- 
nal muscle 
layer. 

Serous  coat. 


Fig.  148. — Longitudinal  section  of 
duodenum  near  pyloric  end,  showing 
glands  of  B  runner. 


The    submucosa 

does  not  differ  from  the  same  layer  already  described 

in  the  wall  of  the  stomach. 


2OO     NORMAL   HISTOLOGY  AND    ORGANOGRAPHY. 


Tania  coll. 


Sacculcs. 


3.  Muscularis. — The  muscularis  consists  of  an 
inner  circular  and  an  outer  longitudinal  layer  of 
smooth  muscle.  The  inner  circular  is  the  heavier  of 
the  two  and  by  its  contraction  produces  many  longi- 
tudinal folds  in  the  mucosa.  Smooth  muscle,  wher- 
ever found,  is  associated  with  connective-tissue 
elements,  but  the  smooth  muscle  of  the  intestine 

has  a  less  suppl} 
of  this  than  the 
smooth  muscle  any 
other  place  in  the 
body. 

4.  Serosa. — This 
layer  is  identical 
with  the  serosa  de- 
scribed  in  the  wall 

Fig.  149.— Portion  of  large  intestine.         of  the  Stomach. 


LARGE  INTESTINE* 

The  average  length  of  the  large  intestine  is  five 
feet.  Its  divisions  are  given  on  page  128.  It  is  dis- 
tinguished from  the  small  intestine  by  the  following 
external  features :  tcznicz  coli,  sacculce,  and  appendices 
epiploiccE. 

TcenicB  Coli. — In  the  large  intestine  the  longitudinal 
muscle  is  gathered  into  three  bands  or  strips  known 
as  taeniae  coli.  Each  band  is  about  one-quarter  inch 
wide  and  one  foot  shorter  than  the  intestine  to 
which  it  belongs.  The  large  intestine,  therefore, 
becomes  sacculated — that  is,  it  is  divided  by  the 
three  longitudinal  muscle  bands  into  three  rows  of 
sacculae.  If  the  bands  be  dissected  away  the  saccules 


DIGESTIVE   SYSTEM. 


201 


Mucosa. 


disappear  and  the  intestine  becomes  about  one  foot 
longer. 

Appendices  epiploiccz  are  small  pedunculate  proc- 
esses that  project  from  the  serous  coat  of  the  large 
intestine.  The  pouches  are  covered  by  the  perito- 
neum and  are  usually  distended  with  fat.  These 
external  features 
are  the  surgeon's 
guide  in  recogniz- 
ing the  large  intes- 
tine. Size  is  a  less 
reliable  factor. 

Structurally  the 
large  intestine  has 
the  same  four  lay- 
ers as  the  small  in- 
testine. The  three 
outer  layers  are 
identical.  The 
mucosa  presents  a 
smooth  surface 
with  numerous  mi- 
nute circular  pits, 


Fig.  150. — Cross  section  of  large  intes- 
tine, showing  many  goblet  cells  in  epithe- 
lium. 


the  crypts  of  Lie- 
berkuhn.  As  villi 
are  absent  the  mu- 
cosa resembles  that  of  the  stomach  rather  than  that  of 
the  small  intestine.  The  crypts  of  the  stomach  are 
shallow,  while  those  of  the  intestine  are  deep  and 
extend  to  the  muscularis  mucosa.  Each  crypt  is 
lined  by  simple  columnar  epithelium.  Goblet  cells 
are  very  numerous  in  this  epithelium. 


202     NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

Vermiform  Appendix. — The  appendix,  although 
very  small,  belongs  to  the  large  intestine.  It  is  a 
worm-like  tube  about  three  inches  long  and  one- 
quarter  inch  thick,  although  the  length  varies 
greatly.  It  is  a  blind  tube  that  evaginates  from 


Fig.  151.  —  Transverse  section  of  human  vermiform  appendix. 
Observe  the  numerous  lymph  nodules.  The  clear  spaces  in  the  submu- 
cosa  are  adipose  tissue  (Sobotta). 

the  lower  end  of  the  cecum.  Lymph  nodes  are 
particularly  abundant  in  the  mucosa  of  the  ap- 
pendix. 

The  following  taken  from  Cunningham's  "Anat- 
omy" will  be  of  interest  to  the  student:  "A  vermi- 
form process  is  found  only  in  man,  the  higher  apes, 


DIGESTIVE  SYSTEM.  203 

and  the  wombat,  although  in  certain  rodents  a 
somewhat  similar  arrangement  exists.  In  carniv- 
orous animals  the  cecum  is  very  slightly  devel- 
oped; in  herbivorous  animals  (with  a  simple  stom- 
ach) it  is,  as  a  rule,  extremely  large.  It  has  been 
suggested  that  the  vermiform  process  in  man  is  the 
degenerated  remains  of  the  herbivorous  cecum, 
which  has  been  replaced  by  the  carnivorous.  An- 
other and  perhaps  more  probable  view  regards  the 
appendix  as  a  lymphoid  organ,  having  the  same 
functions  as  Peyer's  patches  and,  like  these,  under- 
going degeneration  after  middle  life"  (Berry). 

In  the  different  parts  of  the  alimentary  canal  the 
mucosa  shows  a  marked  variation,  as  represented  in 
the  following  table : 


Esophagus. 

Stomach. 

Small  Intestine. 

Large  Intestine. 

Stratified  epithelium. 

Simple  epithelium. 

Simple  epithelium. 

Simple  epithelium. 

Mucous  glands. 

Gastric  glands. 

Brunner's  glands. 

Crypts. 

Crypts  absent. 

Crypts  shallow. 

Crypts  of  Lieber- 

Crypts. 

kiihn. 

Villi  absent. 

Villi  absent. 

Villi  present. 

Villi  absent. 

Valvulae  absent. 

Valvulae  absent. 

Valvulae  conniven- 

Valvulas  absent. 

tes  present. 

Blood  Supply  of  Stomach  and  Intestines. — The  ar- 
teries of  the  stomach  are  all  derived  from  the  celiac 
axis,  a  branch  of  the  aorta.  The  intestines  are  sup- 
plied by  blood  from  the  superior  and  inferior  mesen- 
teric  arteries,  branches  of  the  aorta.  The  arteries 
enter  along  the  line  of  the  mesenteric  attachment 
and  there  form  branches  that  pass  transversely 
around  the  intestine  to  ultimately  penetrate  the 
longitudinal  muscle  layer.  Between  the  two  mus- 
cular coats  branches  are  given  off  to  supply  the 


204      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

muscles  themselves.  The  arteries  then  penetrate 
to  the  submucosa  where  an  extensive  blood  plexus 
is  formed.  From  this  plexus  branches  pass  through 
the  muscularis  mucosa  and  enter  the  mucosa.  Here 


_  Epithelium 
oj  stomach. 


>.  __.  Region  of 
the  bodies 
of  the  gas- 
tric glands. 


-  -Muscularis 


Fig.  r52- — Section  through  fundus  of  cat's  stomach.    The  blood-vessels 
are  injected  (Bohm  and  Davidoff). 


they  branch  into  a  fine  capillary  network  which  in 
the  small  intestine  penetrates  to  the  core  of  the  villi. 
Other  branches  from  this  plexus  supply  the  inner 
portion  of  the  circular  muscle  layer. 

The  veins  lie  side  by  side  with  the  arteries.  Often 
two  veins  accompany  one  artery.  The  blood  drains 
into  the  superior  and  inferior  mesenteric  veins;  the 
inferior  joins  the  splenic,  and  the  latter  unites  with 


DIGESTIVE    SYSTEM.  205 

the  superior  to  form  the  portal  vein.     This  blood 
thus  ultimately  passes  through  the  liver. 

Lymphatics  of  the  Alimentary  Canal. — The  lym- 
phatics begin  in  the  mucosa  just  beneath  the  epithe- 
lium. In  the  small  intestine  they  begin  with  the  cen- 
tral lymph  vessel  of  a  villus.  These  vessels  form  a 
network  in  the  deeper  portion  of  the  mucosa  and 
then  pass  through  the  muscularis  mucosa  to  form 


Fig.  153. — A  portion  of  the  plexus  of  Auerbach  from  stomach  of 
cat,  stained  with  methylene-blue  (intra  vitam),  as  seen  under  low  mag- 
nification (Huber). 

an  extensive  loose  plexus  in  the  submucosa.  Coarser 
lymphatic  vessels  lead  from  this  plexus  through 
the  muscularis,  where  branches  are  received  from  a 
lymphatic  plexus  located  between  the  two  muscle 
coats. 

The  solitary  lymph  nodes  of  the  mucosa  contain 
no  lymphatics,  but  are  encircled  at  their  periphery 


206      NORMAL   HISTOLOGY   AND  ORGANOGRAPHY. 

by  an  extensive  lymphatic  network.  The  same  is 
true  of  the  lymph  nodules  in  Peyer's  patches. 

Nerve  Supply  of  the  Alimentary  Canal. — The  chief 
nerve  supply  of  the  alimentary  tract  consists  of  sym- 
pathetic neurons  whose  nerve  cells  form  the  centers 
of  two  plexuses,  (i)  that  of  Auerbach,  situated 
between  the  two  layers  of  the  muscle  coat,  and  (2) 
that  of  Meissner  in  the  submucosa.  The  latter  con- 
tains fewer  ganglia  and  finer  fibers.  The  numerous 
small  sympathetic  ganglia  of  each  plexus  are  united 
by  small  bundles  of  non-medullated  nerve  fibers  in 
which  a  few  medullated  nerve  fibers  are  present. 
From  these  plexuses  the  nerve  innervation  extends 
to  the  glands  and  epithelial  cells  of  the  mucosa,  and 
to  the  muscularis  to  end  in  small  varicosities  about 
the  smooth  muscle  cells. 

While  the  nerve  innervation  is  not  under  will  con- 
trol it  is  capable  of  being  stimulated  by  cerebro- 
spinal  nerves.  Medullated  nerve  fibers  from  this 
system  have  been  traced  to  terminal  end  baskets 
surrounding  cell  bodies  of  many  of  the  sympathetic 
neurons  of  these  plexuses* 


CHAPTER  V. 
DIGESTIVE  GLANDS. 

SALIVARY  GLANDS. 

i.  Parotid  Gland  (serous  gland). — This  is  a  com- 
pound tubular  gland,  the  largest  of  the  salivary 
glands,  situated  in  the  parotid  recess  at  the  side  of  the 
head  below  and  in  front  of  the  ear.  It  is  a  triangular 
mass  that  varies  in  weight  from  one-half  ounce  to 
one  ounce  or  more.  Its  three  surfaces  are  desig- 
nated as  superficial,  anterior  and  posterior.  The 
gland  is  divided  into  lobes  and  lobules  and  inter- 
laced with  connective-tissue  elements  from  the 
parotid  fascia  that  invests  it. 

The  parotidy  or  Stenson's  duct,  measures  from 
one  and  one-half  to  two  and  one-half  inches  in 
length  and  one-eighth  inch  in  diameter.  It  runs 
forward  across  the  masseter  muscle,  passes  around 
the  anterior  border  of  this  muscle,  pierces  the  buc- 
cinator, then  forward  a  short  distance  to  open  on 
the  inner  surface  of  the  cheek  opposite  the  crown 
of  the  second  upper  molar.  This  duct  is  subject  to 
injury  in  facial  wounds  or  operations. 

The  gland  is  an  epithelial  organ  and  consists  of 
the  excretory  duct,  interlobular ,  intralobular ,  and  in- 
tercalated ducts,  and  the  distal  convoluted  tubules  or 
alveoli.  The  excretory  duct  (Stenson's)  is  lined  by 
stratified  epithelium  near  its  end  where  it  opens  on 

207 


2o8     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

the  mucous  surface  of  the  cheek.  The  rest  of  the 
duct  is  lined  by  two  layers  of  cubical  epithelium, 
which  is  invested  by  a  firm  fibrous  coat  or  tunica 
propria.  The  interlobular  ducts  lie  between  the 


Acini. 


Fig.   154. — Section  through  salivary  gland  of  rabbit,  with  injected 
blood-vessels  (Bohm  and  Davidoff). 

lobules  and  have  much  the  same  histology  as  the 
excretory  duct,  excepting  the  finer  branches  where 
the  epithelium  becomes  simple  cubical.  The  intra- 
lobular  ducts  are  found  inside  the  lobules  and  have  a 
simple  layer  of  tall  cylindrical  cells  whose  cytoplasm 


DIGESTIVE   GLANDS. 


209 


Intralobular  duct. 


shows  a  distinct  longitudinal  striation.  The  inter- 
calated pieces,  on  the  other  hand,  are  clothed  by  a 
single  layer  of  flat,  slender,  often  spindle-shaped 
cells.  The  epithelial  lining  of  the  acini  consists  of 
typical  serous-gland  cells.  This  is  a  single  layer 
of  irregular  columnar  or  cubical  cells  with  nuclei 
situated  near  their  basal  portion.  When  at  rest 
the  cytoplasm  is  filled  with  zymogen  granules 
which  are  used  up  and  largely  disappear  during  the 
process  of  secretion.  Mumps  is  a  specific  disease 
of  this  gland,  more  technically  known  as  parotitis. 

2.  Sublingual  Gland 
(mucous  gland) . — This 
is  really  a  collection  of 
compound  tubulo-alve- 
olar  glands.  It  is  an 
elongated  flattened  mass 
one  and  one-half  to 
one  and  three-quarter 
inches  in  length,  situ- 
ated in  the  floor  of  the 
mouth,  one  on  each  side 
of  the  median  plane,  and  limited  laterally  by  the 
ramus  of  the  mandible.  Its  excretory  ducts,  from 
ten  to  twenty  in  number,  open  separately  on  the 
summit  of  papillae  visible  to  the  naked  eye,  which 
are  situated  just  laterally  to  the  base  of  the  frenum 
of  the  tongue. 

The  duct  system  of  the  gland  is  similar  to  that  of 
the  parotid,  with  the  exception  of  the  intercalated 
piece,  which  is  absent.  The  alveoli  are  less  tubular 
than  those  of  the  parotid  and  are  lined  by  simple 


A  Iveolus. 


Fig.  155. — From  the  parotid  gland 
of  man. 


210     NORMAL  HISTOLOGY    AND   ORGANOGRAPHY. 


columnar  epithelium  with  the  nuclei  situated  at  the 
base  of  the  cells  near  the  basement  membrane. 
These  are  the  chief  cells  of  the  alveoli  and  they  se- 
crete mucus,  which  is  first  stored  up  in  the  cyto- 
plasm in  coarse  granules 
known  as  mucigen,  A 
second  form  of  cells,  less 
numerous,  is  found  singly 
or  in  groups  in  the  periph- 
ery of  the  alveoli  and  in 
close  apposition  to  the 
basement  membrane. 
On  account  of  their  shape 
and  position  they  are 
called  parietal  cells,  cres- 
cents of  Gianuzzi,  or  demi- 
lunes of  Heidenhain. 
They  are  finely  granular, 
stain  red  with  eosin,  and 
are  looked  upon  by  some 
Fig.  156.— Model  of  a  small  as  secreting  a  serous  fluid. 
n:%t%SngeUsalogflaHeid-  There  are  three  theories 

enhain   are    more  deeply   shaded      a§  £Q  their  USC !     ( I )    They 

(Maziarski,  "  Anatomische  Hefte, " 

1901).  may    be    considered     as 

worn-out  chief  cells  that 

have  been  crowded  to  the  basement  membrane  after 
too  active  a  secretion.  (2)  They  may  be  considered 
as  latent  undeveloped  cells  ready  to  take  the  place 
of  mucous  cells  that  get  lost  in  the  process  of  active 
secretion.  (3)  They  may  be  considered  as  normal 
active  cells  contributing  constantly  to  the  salivary 
secretion  in  a  way  that  is  at  present  unknown. 


DIGESTIVE   GLANDS. 


211 


3.  Submaxillary  Gland   (mixed  gland). — In  man 

this  gland  is  composed  of  tubules  having  a  serous 
secretion  and  similar  to  those  of  the  parotid  gland, 
and  tubules  with  alveolar  enlargements  like  the  sub- 
lingual  gland  that  secrete  mucus.  Its  histology, 
therefore,  would  be  a  repetition  of  what  has  already 
been  described  in  the  parotid  and  sublingual  glands. 
The  submaxillary  gland  is  next  in  size  to  the  pa- 
rotid, which  it  resembles  in  color  and  lobulation.  It 


Parietal  cell. 


Acinus. 


Parietal  cell. 


Intralobular  duct.  Interlobular  duct. 

Fig.   157. — Section  from  the  human  submaxillary  gland 

is  placed  against  the  inner  surface  of  the  angle  of  the 
lower  jaw  in  close  proximity  to  the  parotid  gland. 
It  has  a  complete  firm  capsule  derived  from  the  cer- 
vical fascia.  Connective- tissue  elements  from  the 
capsule  ramify  between  the  lobes  and  lobules  of  the 
gland. 

The  submaxillary,  or  Wharton's  duct,  is  about  two 
inches  long,  passes  forward  beneath  the  mylohyoid 
muscle,  then  along  the  inner  side  of  the  sublingual 
gland  to  open  on  the  summit  of  a  small  papilla  situ- 


212      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 


ated  in  the  floor  of  the  mouth  at  the  side  of  the  fre- 
num  of  the  tongue  in  close  proximity  to  its  fellow 
of  the  other  side.  The  submaxillary  gland  of  the 
rabbit  is  a  serous  gland;  that  of  the  dog  and  cat  is 

mucous. 

The  accessory 
salivary  glands  are 
numerous  small 
glands  of  the  mouth 
known  according  to 
their Jocation  as  la- 
bial, palatine,  and 
lingual.  They  are 
mostly  glands  with 
mucous  secretions. 
Branched  tubular 
glands  with  serous 


Fig.  158. — A  number  of  alveoli 
from  the  submaxillary  gland  of  dog, 
stained  in  chrome-silver,  showing  some 
of  the  fine  intercellular  tubules  (Huber). 


secretion    occur  in 
the    tongue,    their 

ducts  opening  into  the  depressions  of  the  circumval- 

late  papillae. 

PANCREAS. 

The  pancreas  is  a  lobulated  compound  racemose 
gland  analogous  in  its  structure  to  the  salivary 
glands.  It  is  situated  transversely  across  the  pos- 
terior wall  of  the  abdomen,  so  deep  in  the  body  and 
so  closely  associated  with  other  organs  that  but 
little  is  known  of  its  diseases.  Its  length  varies 
from  six  to  eight  inches,  its  breadth  one  and  one-half 
inches  and  thickness  from  one-half  to  one  inch.  The 
right  extremity,  or  head,  rests  in  the  concavity  of 


DIGESTIVE   GLANDS. 


213 


the  duodenum  and  the  other  end  touches  the  spleen. 
It  lies  behind  the  peritoneum  and,  unlike  the  salivary 
glands,  it  is  not  enclosed  in  a  fibrous  capsule,  and  is 
therefore  looser  and  softer  in  its  texture. 

The  pancreas  develops  as  two  evaginations  of  the 
alimentary   canal    and    embryologically,    therefore, 


Inter- 
mediate 
tubule. 

Inner 
granular 
zone  of 
secretory 
cells. 


Fig.  159. — From  section  through  human  pancreas  (sublimate)  (Bohm 
and  Davidoff). 

has  two  ducts.  One  of  these,  the  pancreatic  duct, 
or  duct  of  Wirsung,  opens  jointly  with  the  bile  duct 
on  the  summit  of  an  elevated  papilla,  situated  at  the 
inner  side  of  the  descending  portion  of  the  duodenum. 
This  duct  extends  the  length  of  the  pancreas  and 
receives  in  its  course  the  short  ducts  from  the  various 
lobes  composing  the  gland. 


214      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY, 


The  second  duct,  or  duct  of  Santorini,  loses  its 
connection  with  the  alimentary  canal  and  comes  to 
open  into  the  duct  of  Wirsung.  It  is  a  very  short 
tube,  inferior  in  position  and  secondary  in  impor- 
tance. 

Histologically,  the  ducts  are  lined  by  a  mucous 
membrane  of  simple  columnar  epithelial  cells  that 
are  morphologically  continuous  and  analogous  with 
the  epithelial  cells  of  the  intestine.  This  mucous 


Connective  tissue. 

r..  Centro-acinal  cell. 
Secretory  cell. 
Intermediate  duct. 


Fig.  1 60.  —  Scheme  showing  relation  of  three  adjoining  alveoli  to 
excretory  duct,  illustrating  origin  of  centro-acinal  cells  (Bohm  and 
Davidoff). 

membrane  is  ensheathed  by  a  coat  of  connective- 
tissue  elements,  fibers  and  cells,  all  of  which  are 
associated  with  more  or  less  fat. 

The  acini  resemble  in  form  and  size  those  of  the 
salivary  glands.  The  parietal  cells  are  absent.  The 
chief  cells  are  columnar,  the  nucleus  near  the  base  of 
the  cell,  and  the  cytoplasm  loaded  with  zymogen 
granules.  During  physiological  activity  these  gran- 
ules are  greatly  reduced.  In  addition,  centro-acinal 


DIGESTIVE   GLANDS. 


215 


cells  are  present.  These  are  smaller  and  flatter 
than  the  chief  cells  and  occupy  a  central  position  of 
many  acini.  They  represent  an  invagination  of  the 
neck  of  the  acinus  and  are  best  understood  by  re- 
ferring to  Fig.  1 60. 

Areas  of  Langerhans.- — These  are  oval  cell  masses 
that  measure  0.2  to  0.3  mm.  They  are  found  in  the 
lobules  of  the  pancreas,  always  associated  with  the 
connective  tissue  but  having  no  connection  with  the 


Pancreatic  duct. 


Acinus. 


Blood  capil- 
laries. 


Connective  tissue.  Area  of  Langerhans. 

Fig.  161. — Section  from  an  injected  pancreas  of  the  dog. 

pancreatic  tubules.  The  areas  are  surrounded  by  a 
rich  supply  of  coarse  capillary  blood-vessels.  The 
individual  cells  are  epithelioid,  smaller  than  those 
of  the  acini,  arid  finely  granular.  In  many  respects 
they  resemble  the  liver  cells.  It  is  believed  that  the 
secretions  from  these  cells  is  absorbed  by  the  blood 
and  modifies  the  distribution  and  elimination  of 
sugar.  The  areas  thus  have  a  compensatory  rela- 
tion to  the  liver  and  may  do  in  part  the  work  of  that 
organ.  A  marked  disturbance  in  these  areas  has 


2l6      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

been  observed  in  diabetes,  but  whether  a  cause  01 
consequence  is  not  known. 

LIVER. 

The  liver  is  a  large  compound  tubular  gland  whose 
terminal  ducts  anastomose.  In  this  respect  it  differs 
from  any  other  gland  in  the  body.  It  develops  as  a 
ventral  evagination  of  the  intestinal  wall  and  in 
close  proximity  to  the  origin  of  the  pancreas,  so  that 
in  the  adult  the  ducts  of  these  two  organs  have  a 


Non-peritoneal 


Tuber   omen-   — 

tale.  ^isis 

Impressio  celica. 


Impressio  pylorica. 
Fig.  162. — Posterior  and  inferior  surfaces  of  the  liver  (Nancrede). 

common  opening  at  the  apex  of  a  papilla,  as  already 
mentioned  in  the  description  of  the  pancreas.  If  an 
obstruction  occurs  at  this  opening,  it  is  possible  for 
the  pent-up  bile  to  invade  the  pancreas.  The  ven- 
tral liver  diverticulum  quickly  bifurcates  to  form 
respectively  the  right  and  left  lobes  of  the  liver. 
By  repeated  divisions  the  bile  system  of  the  organ  is 
built  up,  forming  an  elaborate  anastomosis  of  the 
finer  bile  capillaries.  It  follows,  therefore,  that  the 
liver  cells  are  genetically  related  to  the  pancreatic 


DIGESTIVE   GLANDS. 


217 


cells  and  sister  cells  of  the  columnar  epithelium  of 
the  alimentary  tract. 

The  fully  developed  liver  consists  of  five  lobes: 
right  lobe,  left  lobe,  quadrate,  caudate,  and  spigelian 
lobes.  Five  fissures:  umbilical,  ductus  venosus, 
transverse,  gall  bladder,  and  vena  cava  fissures.  Five 
ligaments :  ligamentum  teres  (remnant  of  the  umbilical 
vein),  falciform,  coronal,  and  two  lateral  ligaments. 


Interlobular  -vein. 


p  Interlobular  bile  duct. 

Intralobular  bile  duct. 
Liver  cells. 

jr-  Intralobular  vein. 


Sublobular  vein. 
Fig.  163. — Diagram  of  liver  lobule. 

The  description  of  these  structures  belongs  to  gross 
anatomy. 

The  liver  is  the  largest  gland  in  the  body,  weigh- 
ing from  three  to  four  pounds,  or  one-fortieth  the 
weight  of  the  whole  body.  It  measures  ten  to 
twelve  inches  in  its  transverse  diameter,  six  to  seven 
inches  in  its  antero-posterior,  and  about  three  inches 
thick  at  the  back  part  of  the  right  lobe,  which  is  the 


2l8      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY 

thickest  part.  This  heavy  organ  is  held  in  position 
not  only  by  its  ligaments  but  by  the  abdominal  pres- 
sure, and  also  by  the  connective  tissue  of  the  vena 
cava,  which  forms  a  dorsal  fissure  between  the  right 
and  left  lobes. 

The  organ  is  enclosed  in  a  firm  connective-tissue 
capsule  (capsule  of  Glissori) ,  which  is  very  dense  over 
the  lower  surface  in  the  region  of  the  fissures,  par- 


Interlobular  vein. 
Blood  capillaries. 

Intralobular  vein. 
Cord  0}  liver  cells. 


Fig.  164. — Injected  blood-vessels  in  liver  lobule. 

ticularly  the  transverse,  where  the  blood-vessels  and 
bile  duct  enter.  Septa  from  this  capsule  ramify 
between  the  lobes  and  lobules,  and  finer  branches 
interlace  between  the  liver  cells,  giving  everywhere 
support  and  consistency  to  the  organ.  Here,  as  in 
every  organ,  blood-vessels,  lymph- vessels,  and  fat  are 
associated  with  this  connective-tissue  fabric.  The 
capsule  is  closely  invested  with  peritoneum,  except- 
ing a  circular  area  bounded  by  the  coronal  ligament, 


DIGESTIVE   GLANDS. 


where  the  capsule,  and  therefore  the  liver,  is  in  direct 
apposition  with  the  lower  surface  of  the  diaphragm. 
The  blood  supply  of  the  liver  consists  of  the  hepatic 
artery,  and  a  branch  of  the  celiac  axis,  and  the  portal 
vein,  formed  by  the  junction  of  the  splenic  and  supe- 
rior mesenteric  veins.  The  portal  vein  is  by  far  the 
larger  vessel.  These  vessels  accompany  the  bile- 


j,  Intralobular 
vein. 

-   Branch  of 

Portal  vein. 
"  Bile  duct. 

Branch  of  he- 
Patic  artery. 


Fig.   165. — Section  through  liver  of   pig,  showing  chains  of   liver-cells 
(Bohm  and  Davidoff). 


duct,  and  wherever  one  branches  the  others  do,  even 
to  the  finer  terminations  between  the  liver  lobules. 
The  duct,  vein  and  artery  form  the  ventral  border 
of  the  foramen  of  Winslow.  Their  relation  at  this 
place  is,  bile  duct  to  the  right,  artery  to  the  left,  and 
vein  between  and  behind  the  other  two.  This  rela- 
tion is  an  important  one  in  the  surgery  of  these  parts. 


220     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

The  Portal  Canal. — This  consists  of  an  artery,  a 
bile  duct,  and  a  vein,  with  accompanying  lymphatics 
and  connective  tissue.  Sections  of  the  portal  canal 
may  be  found  between  the  liver  lobules  where  the 
vessels  are  small,  or  between  the  liver  lobes  where  the 
structures  are  large.  The  bile  duct  can  be  recog- 
nized by  the  columnar  simple  epithelium  and  the 
artery  and  vein  by  their  respective  histology.  In 


Boundary  - 
of  lobule. 


Fig.  1 66. — Reticulum  (Gitterfasern)  of  dog's  liver  (gold-chlorid  method) 
(Bohm  and  Davidoff). 

pathological  sections,  where  the  lobules  can  no 
longer  be  recognized,  the  portal  canal  usually  re- 
mains patent  and  is  therefore  a  valuable  criterion 
in  the  identification  of  this  tissue. 

The  common  bile  duct  is  formed  by  the  junction  of 
the  hepatic  and  cystic  ducts  at  the  mouth  of  the 
transverse  fissure,  and  passes  downward  anterior  to 


DIGESTIVE    GLANDS.  221 

the  foramen  of  Winslow  to  open  into  the  descending 
part  of  the  duodenum  three  and  one-half  to  four 
inches  beyond  the  pylorus.  It  passes  obliquely 
through  the  intestinal  wall,  where  it  is  joined  by  the 
pancreatic  duct,  and  opens  by  a  common  orifice  on 
the  bile  papilla,  as  already  described.  The  common 
bile  duct  is  about  three  inches  long  and  one-quarter 
inch  in  diameter. 

The  histology  of  the  bile  ducts  resembles  that  of  the 
gall  bladder.     There  is  on  the  inside  a  mucous  mem- 
brane  clothed  with  simple  columnar  epithelium  rest- 
ing upon  a  base- 
ment  membrane.  Lymphatics. 

\\ 

Smooth  muscle 

cells  are  found  in      tl/  vw^ 

X  \W&®%*&& Bile  duct. 

the    membrana 


propriaof  themu- 
cosa.      The    sub-      ^ 
mucosa  is  a  nar- 
row Vascular  layer        Fig.  167. — Section  of  portal  canal  of  liver. 

composed  of  con- 
nective-tissue elements.  The  muscularis  consists  of 
an  inner  circular  layer  and  an  outer  longitudinal 
layer  of  smooth  muscle.  On  the  outside  is  a  strong 
connective-tissue  coat  whose  fibers  are  continuous 
with  the  capsule  of  Glisson. 

The  passage  of  bile  into  the  intestine  is  not  a  pas- 
sive but  an  active  process.  The  smooth  muscle  of 
the  bile  duct  contracts  in  a  peristaltic  manner,  and 
the  bile  is  thus  expelled  into  the  intestine,  periodi- 
cally, in  jets.  This  activity  is  normally  under  con- 
trol of  the  nerves,  largely  a  reflex  action  of  the  sym- 


222      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

pathetic  nerves  associated  with  the  intestine.  If 
there  is  an  obstruction  to  the  free  passage  of  bile,  as 
in  the  passage  of  a  calculus,  the  musculature  of  the 
ducts  contracts  violently  and  spasmodically,  giving 
rise  to  the  characteristic  pain  of  plain  muscle  con- 
traction described  on  page  94.  If  the  obstruction 
occurs  in  the  hepatic  or  the  common  duct,  the  liver 
becomes  saturated  with  bile  which  is  absorbed  by  the 
blood,  and  jaundice  follows.  If  the  obstruction  is 
in  the  cystic  duct  the  liver  does  not  suffer  and  there  is 
no  jaundice. 

Smaller  Excretory  Bile  Ducts  and  Gall  Bladder- 
Small  bile  ducts  of  the  liver  begin  within  the  liver 
lobules,  where  they  form  a  complex  system  of  anas- 
tomosing channels  or  tubes  called  bile  canaliculi. 

Interlobular  Ducts. — The  bile  canaliculi  unite  to 
form  interlobular  ducts  that  lie  between  the  liver  lob- 
ules. These  unite  into  larger  and  larger  ducts  and 
converge  to  pass  out  through  the  transverse  fissure, 
where  five  or  six  ducts  are  found.  The  latter  unite 
into  two  short  main  ducts  that  drain  respectively 
from  the  right  and  left  lobes  of  the  liver. 

The  hepatic  duct  is  formed  by  the  union  of  the  two 
main  ducts  at  the  bottom  of  the  transverse  fissure 
and  thus  receives  the  bile  from  the  whole  liver.  It  is 
from  one  to  one  and  one-quarter  inches  in  length  and 
one-quarter  inch  in  breadth,  and  extends  downward 
from  its  origin,  taking  an  irregular  course,  to  its 
junction  with  the  cystic  duct,  which  unites  with  it  to 
form  the  common  bile  duct. 

The  gall  bladder,  with  its  cystic  duct,  is  an  evagina- 
tion  of  the  bile  duct.  The  gall  bladder  is  a  pear- 


DIGESTIVE   GLANDS. 


223 


shaped  receptacle  for  the  retention  of  bile,  and  has  a 
fundus,  body,  and  neck.  It  is  usually  about  three 
inches  in  length  and  one  to  one  and  one-quarter 
inches  in  diameter  with  a  normal  capacity  of  one  to 
one  and  one-half  fluidounces.  Structurally  it  has 
an  outer  coat  of  perito- 
neum, a  middle  coat 
of  connective  -tissue 
elements,  with  a  liberal 
mixture  of  smooth 
muscle  fibers,  and  an 
inner  coat  of  mucous 
membrane  raised  into 
folds  and  covered  with 
simple  columnar  epi- 
thelium. 

The  cystic  duct  begins 
at  the  neck  of  the  gall 
bladder  and  extends 
downward  to  its  junc- 
tion with  the  hepatic 
duct,  with  which  it 


Fig.  1 68. — Portion  of  gall  bladder 
and  bile  ducts:  i,  Cavity  of  gall 
bladder;  2,  cavity  of  calyx;  3,  groove 
separating  the  calyx  from  the  bladder; 
4,  promontory;  5,  superior  valve  of 
calyx:  6,  cystic  canal;  7,  common 
bile  duct;  8,  hepatic  duct  (Testut). 


forms  an  acute  angle. 

It  takes  an    irregular 

course  and  is  from  one 

and  one-quarter  to  one 

and     one-half     inches 

long;    therefore  longer 

than  the  hepatic  duct,  but  only  about  one-half  its 

diameter. 

Liver  Lobules. — These  are  minute  units  of  the  liver 
about  the  size  of  a  pinhead.     They  are  cylindrical 


224      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 


or  irregularly  polyhedral  in  shape,  about  2  mm.  in 
length  and  i  mm.  in  breadth.  Their  arrangement 
is  quite  irregular  except  just  beneath  the  capsule 
where  they  usually  lie  with  their  apices  toward  the 
surface.  Each  lobule  has  a  connective-tissue  in- 
vestment in  which  the  finer  branches  of  the  portal 


Blood  capil- 
laries. 


-  -  Cord  of  he- 
patic  cells. 


Interlobular 

vessel. 


Fig.  169. — Injected  blood-vessels  in  liver  lobule  of  rabbit  (Bohm  and 

Davidoff). 

canal  ramify.  This  investment  is  particularly  dense 
in  the  pig,  which  renders  the  organ  in  this  animal 
very  fibrous  and  tough,  quite  unfit  for  the  market. 
In  certain  chronic  liver  diseases  the  same  condition 
obtains,  when  the  organ  is  spoken  of  as  the  "  hob- 
nailed'' or  " nutmeg"  liver. 


DIGESTIVE   GLANDS. 


225 


In  the  center  of  each  lobule  is  a  blood-vessel  known 
as  the  intralobular  vein,  while  the  small  veins  be- 
tween the  lobules  are  called  the  interlobular  veins. 
These  two  sets  of  veins  are  connected  by  irregular 
blood  capillaries  that  radiate  from  the  periphery  of 
the  lobule  to  its  center.  They  are  typical  capillaries 
whose  walls  consist  of  but  a  single  layer  of  flattened 


3^7^-  Intralobular 
vein. 


Fig.  1 70. — Human  bile  capillaries.  The  capillaries  of  one  lobule  are 
seen  to  anastomose  with  those  of  the  adjoining  lobule  (below,  in  the 
figure)  (chrome-silver  method)  (Bohm  and  Davidoff). 

endothelial  cells.  The  blood  in  the  portal  vein 
passes  to  the  interlobular  veins,  then  through  the 
capillaries  to  the  intralobular  vein.  The  latter 
opens  into  sublobular  veins  which  unite  to  form  the 
hepatic  veins,  and  these  in  turn  open  into  the  vena 
cava  just  below  the  diaphragm.  The  arterial  blood 
of  the  hepatic  artery  supplies  the  connective  tissues, 
15 


Fig.  i7i.-Schematic  diagram 
of  hepatic  cord  in  transverse  sec- 
tion.  At  the  left  the  bile  capillary 
is  formed  by  four  cells,  at  the  right 


226      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

the  walls  of  the  bile  ducts  and  blood-vessels,  and 
doubtless  some  of  this  arterial  blood  finds  its  way 

into  the  liver  capillaries 
where  it  blends  with  the 
venous  blood  from  the 
portal  vein. 

From  the  center  of  each 
lobule  toward  its  periph- 
ery irregular  strands  of 
liver  cells  radiate  ana 
freely  anastomose  with 
Davidoff).  each  other,  as  well  as  in- 

terlace between  the  blood 

capillaries.  These  are  called  hepatic  cords  and  con- 
sist of  double  irregular  rows  of  liver  cells.  The 
cords  constitute  the 
bile  capillaries  and 
unite  at  the  periph- 
ery of  the  lobule 
with  the  bile  ducts 
of  the  portal  canal, 
situated  between  the 
lobules.  The  bile 
capillaries,  there- 
fore,  are  very  fine 
tubes  lying  between 
the  liver  cells  that 
constitute  its  walls. 
These  tubes  anasto- 
mose freely  with 
each  other  and  are  the  terminal  endings  of  the  bile 
passages  or  its  secreting  portions.  The  liver,  as  a 


Bile  capillaries. 


Fig.  172. — From  the  human  liver, 
showing  the  beginning  of  the  bile  ducts 
(chrome-silver)  (Bohm  and  Davidoff). 


PLATE  V. 


DIGESTIVE   GLANDS. 


227 


Intercellular  bile 
duct. 


Fig.  173. — Diagram  of  liver  cells,  show- 
ing bile  passages. 


gland,  thus  differs  from  all  other  glands  (i),  that  the 
secreting  tubules  anastomose,  and  (2)  that  the  wall 
of  the  secreting  portions  consists  of  but  two  cells. 
The    liver  cells 

have    no     Cell    Wall.  —      Intracellular  bile  passage. 

They  are  large  poly- 
hedral or  irregular 
epithelial  cells,  con- 
taining sometimes 
two,  but  usually  one, 
nucleus.  The  cyto- 
plasm is  granular, 
containing  bile  drops 
and  vacuoles.  The 
chief  function  of 
these  cells  is  twofold :  (i)  to  secrete  bile  into  the  bile 
capillaries,  and  (2)  receive  and  contribute  sugar  to  the 
blood  capillaries.  In  junction  with  this  it  is  affirmed 

that     definite    cyto- 
capillary.  plaswiic  or  intracellu- 

lar  channels  exist, 
particularly  for  the 
passage  of  bile. 
These  channels  end 
in  minute  dilatations 
within  the  cells,  from 
which  finer  passages 
lead  to  and  arborize 
around  the  nucleus. 
According  to  some 

investigators,  the  finer  passages  may  penetrate  the 
nucleus  and   are   then   called   intranuclear    canals. 


Intercellular  bile  duct. 


Intracellular  bile 
passage. 


Blood  capillaries. 

Fig.    174. — Diagram    of    liver   cells, 
showing  bile  ducts  and  blood  capillaries. 


228      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


Fig.  175. — From  preparation  from  the  liver  of  a  rabbit,  showing 
the  so-called  stellate  cells  of  Kupffer:  a,  Stellate  cells;  b,  liver  cells 
(Huber). 


Fig.  176. — Part  of  a  section  through  liver  lobule  from  dog,  showing  stel 
late  cells  (Bohm  and  Davidoff). 


DIGESTIVE   GLANDS.  2 29 

Whether  this  intracellular  system  is  an  artifact  due 
to  manipulations  or  a  normal  condition  is  at  present 
unsettled.  In  either  case  the  liver  cells  play  a  deli- 
cate role,  and  a  slight  functional  disturbance  may 
allow  the  bile  to  escape  to  the  blood  capillaries,  with 
jaundice  as  a  natural  sequel.  In  such  a  case  there 
may  or  may  not  be  any  pain  depending  on  the  pres- 
ence or  absence  of  an  obstruction  in  the  bile  duct. 

Stellate  Cells  of  Kupffer. — These  are  uniformly 
distributed  in  the  lobules.  The  cells  are  irregular, 
elongated,  and  end  in  two  or  three  pointed  projec- 
tions. They  are  smaller  than  the  hepatic  cells  and 
are  seen  only  after  a  special  method  of  treatment. 
According  to  Kupffer  these  cells  belong  to  the  endo- 
thelium  of  the  intralobular  blood  capillaries,  and 
possess  a  phagocytic  function. 

Lastly,  each  lobule  is  interlaced  by  a  fine  reticular 
connective  fabric  that  comes  from  the  connective- 
tissue  investment  of  the  lobule.  This  gives  support 
and  consistency  to  the  lobule. 

Lymphatics  of  the  Liver. — These  may  be  divided 
into  (i)  the  interlobular  lymphatics,  which  accom- 
pany and  in  some  places  surround  the  blood-vessels, 
and  (2)  sub  peritoneal  lymphatics  on  the  surface  of 
the  organ  which  in  the  upper  portions  communicate 
through  the  ligaments  with  the  thoracic  lymphatics. 

Nerves  of  the  Liver. — The  liver  receives  medullated 
fibers  from  the  left  pneumogastric  and  non-medul- 
lated  fibers  from  the  solar  plexus.  The  nerves  reach 
the  organ  between  the  two  layers  of  the  small  omen- 
turn  and  accompany  the  portal  canal,  therefore  enter 
the  liver  at  the  transverse  fissure.  The  sympathetic 


230      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

fibers  innervate  the  walls  of  the  blood-vessels.  The 
medullated  pass  to  the  liver  lobules  where  they  lose 
the  medullary  sheath  and  then  accompany  the  he- 
patic cords  or  bile  capillaries  to  ramify  ultimately 
between  and  around  the  liver  cells. 


CHAPTER  VI. 

ORGANS  OF  RESPIRATION  AND  THYROID 
GLAND. 

The  organs  of  respiration  comprise  the  larynx, 
trachea,  bronchi  and  lungs.  More  than  forty  per 
cent,  of  all  deaths  are  directly  due  to  diseases  of  this 
tract,  which  renders  a  thorough  knowledge  of  this 
system  of  primary  importance.  These  organs  de- 
velop as  a  ventral  median  outgrowth  of  the  fore-gut, 
and  the  mucous  epithelium  is  therefore  derived  from 
the  entoderm.  The  primitive  connection  with  the 
alimentary  canal  is  maintained  in  the  adult,  the  upper 
extremity  of  the  larynx  opening  on  the  anterior  wall 
of  the  pharynx. 

THE  LARYNX. 

The  larynx  in  the  male  averages  44  mm.  in  length, 
43  mm.  transverse  diameter,  and  36  mm.  antero- 
posterioF  diameter.  In  the  female  these  dimensions 
are  36  by  41  by  26  mm.  It  is  a  cartilaginous  mus- 
cular tube  that  contains  the  two  vocal  cords,  the  latter 
being  transverse  folds  of  mucous  membranes. 

In  the  wall  are  three  single  symmetrical  cartilages, 
the  thyroid,  cricoid,  and  cartilage  of  the  epiglottis;  and 
three  pairs,  namely,  two  arytenoids,  two  corniculce 
laryngis  (cartilages  of  Santorini),  and  two  cuneiform, 
making  in  all  nine  pieces.  The  two  last  pairs  are  very 

231 


232      NORMAL   HISTOLOGY   AND  ORGANOGRAPHY. 

small,  while  only  the  thyroid  and  cricoid  are  visible 
on  the  front  and  sides  of  the  larynx.  The  cartilage 
of  the  epiglottis,  the  arytenoids,  the  corniculae  laryn- 


Fig.  177. — Articulations  and  liga- 
ments of  the  larynx,  anterior  view: 
A,  Hyoid  bone,  with  a  its  greater, 
and  a'  its  lesser  cornua;  1-5,  liga- 
ments; 6,  lateral  cricothyroid  artic- 
ulation; 7,  junction  of  cricoid  and 
trachea  (Testut). 


Fig.  178. — Articulations  and  lig- 
aments of  the  larynx,  posterior 
view:  A,  Hyoid;  B,  thyroid,  with 
b  and  bf  its  cornua;  C,  cricoid;  D, 
arytenoids;  E,  cartilages  of  San- 
torini;  F,  epiglottis;  G,  trachea; 
1-6,  ligaments;  2,  opening  for  su- 
perior laryngeal  artery;  7,s  junc- 
tion of  trachea  and  cricoid  (Tes- 
tut). 


gis,  are  of  the  elastic  or  yellow  fibrous  variety  and  do 
not  tend  to  ossify  with  age.  The  rest  are  composed  of 
the  hyaline  cartilage,  which  tends  to  ossify  with  age. 
Many  pairs  of  muscle  control  the  manipulation  of 


ORGANvS    OF   RESPIRATION. 


233 


these   cartilages,    regulating   the   vocal   cords   and 
modulating  the  voice. 

The  mucous  membrane  of  the  larynx  is  continuous 


Glands  in  false 
vocal  cord. 


Stratified  pavement  .._ 
epithelium  of  true  \ 
vocal  cord. 


Stratified  ciliated  col- 
umnar epithelium. 


Glands. 


Muscle. 


Muscle. 


Fig.  179. — Vertical  section  through  the  mucous  membrane  of  the  human 
larynx  (Bohm  and  Davidoff). 

with  that  of  the  mouth  and  particularly  sensitive 
about  the  upper  part  above  the  glottis.     This  mu- 


234      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


cous  membrane  is  covered  in  the  greater  part  of  its 
extent  with  stratified  columnar  ciliated  epithelium. 
The  cilia  are  found  higher  up  the  front  wall  than  on 
each  side,  reaching  in  the  former  to  the  base  of  the 
epiglottis  and  at  the  sides  to  a  point  just  above  the 
false  vocal  cords.  Above  these  points  the  epithelium 
is  stratified  squamous,  like  that  of  the  pharynx. 

Upon  the  true  vo- 
cal cords  the  epi- 
thelium is  also 
stratified  squa- 
mous. Mucous 
glands  are  found 
everywhere  in 
this  membrane 
but  are  particu- 
larly abundant 
upon  the  epiglot- 
tis. 

The  membrana 
propria,  on  which 
the  epithelial  cells 
rest,  is  not  only 
very  vascular  but 
has  a  rich  supply 


Fig.  1 80. — Diagram  to  illustrate  the 
thyro-arytenoid  muscles;  the  figure  repre- 
sents a  transverse  section  of  the  larynx 
through  the  bases  of  the  arytenoid  carti- 
lages: Ary,  arytenoid  cartilage;  p.m,  proc- 
essus  muscularis;  p.v,  processus  vocalis; 
Th,  thyroid  cartilage;  c.v,  vocal  cords;  Oe 
is  placed  in  the  esophagus;  m.thy.ar.i,  in- 
ternal thyro-arytenoid  muscle;  m.thy.ar.e,  ex- 
ternal thyro-arytenoid  muscle;  m.thy.ar.ep, 
part  of  the  thyro-ary-epiglottic  muscle,  cut 
more  or  less  transversely;  m.ar.t,  transverse 
arytenoid  muscle.  (Redrawn  from  Foster.) 


of    elastic    fibers 

and  other  connective-tissue  elements.  It  is  this  tis- 
sue that  becomes  edematous  and  greatly  swollen  in 
infections,  such  as  diphtheria.  This  is  nature's 
method  of  eliminating  the  disease,  with,  however,  the 
accompanying  danger  of  suffocation. 

The  vocal  cords  are  transverse  elastic  ligaments 


ORGANS   OF   RESPIRATION. 


235 


Vein. 


covered  with  a  very  thin  mucous  membrane.  They 
are  attached  anteriorly  to  the  thyroid  cartilage, 
close  to  each  other,  and  diverge  posteriorly  to  their 
attachment  in  the  arytenoid  cartilages.  The  glottis 
is  the  slit-like  opening  between  the  vocal  cords. 

THE  THYROID  GLAND. 

The  thyroid  gland  is  not  a  part  of  the  respiratory 
tract,  but  it  is  so  closely  associated  with  this  tract  in 
development  and  in  position  that  it  seems  advisable 
to  describe  the 
organ  in  this 
place.  The  gland 
is  a  highly  vas- 
cular body  con- 
sisting of  twro  lat- 
eral lobes  and 
connected  by  a 
transverse  bar, 
the  isthmus .  The 
rudiments  of  the 
lobes  develop 
from  the  epithe- 
lium of  the  fourth  gill  cleft,  while  the  isthmus  and  a 
large  part  of  the  lobes  come  from  the  floor  of  the 
mouth,  the  thyroglossus  duct  at  the  base  of  the 
tongue  being  a  remnant  of  this  origin.  The  gland 
is  therefore  an  epithelial  organ  derived  from  the  ento- 
derm. 

In  position  the  gland  lies  low  down  in  the  neck 
and  in  close  apposition  to  the  trachea.  The  isthmus 
crosses  in  front  of  the  trachea  and  covers  the  second 


Artery. 


Colloid. 


Connective  tissue. 

Fig.  181. — Section  from  thyroid  gland,  show- 
ing vesicles  or  alveoli. 


236      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

and  third  cartilage  ring.  The  lateral  lobes  are  closely 
applied  to  the  sides  of  the  trachea  and  extend  up- 
ward to  cover  the  lower  part  of  the  thyroid  cartilage. 
Each  lobe  measures  about  two  inches  in  length,  one 
and  one-quarter  inches  in  breadth,  and  one-half  inch 
in  depth.  The  gland,  however,  is  subject  to  great 
variations  both  in  size,  form,  and  position.  It  is  gen- 
erally larger  in  females,  and  appears  to  undergo  a 
periodic  enlargement  during  each  menstruation.  It 

reaches  its  maxi- 
mum growth  at  pu- 
berty, and  is  fre- 
quently much  di- 
minished in  size  in 
old  age. 

Structure.— The 

vv   -..-,   -*  -.  f thyroid  gland  is  in- 

vested  by  a  thin 
layer  of  areolar  tis- 
sue which  not  only 
binds  it  fast  to  the 
trachea,  but  divides 

Fig.  182.— Portion    of  a  cross    sec-        it  into  Small  lobules 
tion  of  thyroid  gland  of  a  man;   c,  col-  . 

.  loid  substance  (Sobotta).  of  irregular  size  and 

form.  It  is  a  duct- 
less gland  consisting  of  epithelial  vesicles  varying  in 
size  from  .05  mm.  to  i  mm.  in  diameter.  These  vesi- 
cles vary  greatly  in  form  and  are  grouped  and  held  to- 
gether by  areolar  connective  tissue  in  which  many 
blood-vessels  ramify.  These  vesicles  are  generally 
filled  with  colloid  substance,  a  yellow  viscid  fluid,  that 
in  sections  stains  a  yellowish  red  with  eosin.  They  are 


ORGANS   OF   RESPIRATION.  237 

lined  by  a  simple  cubical  epithelium  made  up  of  two 
kinds  of  cells,  (i)  a  smaller  number  of  colloid  cells 
engaged  in  the  production  of  colloid,  and  (2)  inter- 
vening chief  cells  which  replace  the  former  in  case 
they  are  lost.  It  is  affirmed  by  some  that  the  two 
kinds  of  cells  represent  merely  different  stages  of 
secretion. 

The  thyroid,  being  an  epithelial  organ,  may  be  the 
seat  of  a  cancer.  Goiter  is  a  more  common  thyroid 
tumor,  consisting  of  accumulations  within  its  vesi- 
cles of  colloid  substance;  or  an  increase  of  the  con- 
nective-tissue elements;  or  a  multiplication  of  the 
thyroid  vesicles.  Removal  of  the  thyroid  produces 
myxedema,  while  a  congenital  absence  of  the  gland 
is  the  cause  of  cretinism.  In  the  latter  case,  thyroid 
extract,  regularly  administered,  will  establish  a  nor- 
mal growth  of  the  child.  In  exophthalmic  goiter  the 
thyroid  gland  is  enlarged,  but  in  this  case  the  en- 
larged thyroid  is  a  symptom  of  a  more  general  disease 
involving  other  organs  and  systems.  The  thyroid 
gland  may  be  removed  and  grafted  almost  anywhere 
in  the  body.  It  will  readily  grow  in  its  new  position 
and  assume  its  normal  function  with  good  results. 

Vessels  and  Nerves. — The  arteries  of  the  thyroid 
gland  are  the  superior  and  inferior  thyroid  arteries  on 
each  side,  to  which  is  sometimes  added  a  fifth  vessel, 
the  thyroidea  ima.  The  organ  has,  therefore,  a  very 
rich  supply  of  blood.  The  smaller  vessels  and  capil- 
laries ramify  in  the  connective-tissue  elements  be- 
tween the  gland  vesicles.  The  veins,  which  are  also 
large,  form  an  extensive  plexus  near  the  surface  of 
the  gland,  from  which  a  superior,  middle,  andinferior 


238     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

vein  are  formed  on  each  side.  Extensive  lymphatics 
accompany  the  blood  system.  The  nerves  are  derived 
from  the  middle  and  inferior  cervical  ganglia  of  the 
sympathetic.  They  accompany  the  blood-vessels, 
whose  walls  they  innervate,  sending  also  branches 
that  extend  close  to  the  base  of  the  epithelial  cells. 

PARATHYROIDS* 

The  parathyroids  are  two  flattened  bodies,  one- 
fourth  to  one-half  inch  in  diameter,  that  are  con- 


Fig.   183. — From  parathyroid  of  man  (Huber.) 

stantly  present  and  placed  in  close  proximity  to  the 
upper  and  posterior  surface  of  the  lobes  of  the  thy- 
roid gland.  They  consist  of  solid  masses  of  epithelial 
cells.  Lymphoid  follicles  are  usually  closely  asso- 
ciated with  these  masses.  The  function  of  these 
little  bodies  is  not  known;  however,  if  the  thyroid 
gland  be  removed  and  the  parathyroid  left,  the  effect 
of  a  complete  thyroidectomy  is  not  obtained. 


ORGANS   OF   RESPIRATION. 


239 


THE  TRACHEA  AND  BRONCHI. 
The  trachea  extends  from  the  cricoid  cartilage,  a 
point  opposite  the  lower  border  of  the  sixth  cervical 
vertebra,  to  the  level  of  the  intervertebral  disc  be- 


Thyroid  cartilage. 


Crico-thyroid  membrane. 
Cricoid  cartilage. 
Thyroid  gland. 


Epartenal 
bronchus. 


Hyparterial  bronchus. 
Fig.   184. — The  trachea  and  bronchi. 

tween  the  fourth  and  fifth  dorsal  vertebrae,  extend- 
ing therefore  one  to  two  inches  into  the  chest.     The 


240      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


trachea  measures  from  four  to  four  and  one- half 
inches  in  length,  and  three-fourths  to  one  inch  in 
width.  It  is  smallest  at  its  commencement,  and, 
although  quite  uniform  in  its  dimensions,  is  usually  a 
little  wider  midway  between  its  two  ends. 

At  the  lower  end  the  trachea  bifurcates  to  form 
the  right  and  left  bronchi,  which  pass  each  to  the  root 

of  the  corresponding 
lung.  The  right  bron- 
chus is  larger  than 
the  left  and  more 
nearly  vertical,  so  that 
in  looking  down  the 
trachea  more  of  the 
right  than  of  the  left 
bronchus  can  be  seen. 
The  right  bronchus  di- 
vides into  branches, 
one  to  each  root  of 
the  three  lobes  of  the 
right  lung,  while  the 
left  gives  off  two 
branches,  one  to  each 
lobe  of  the  left  lung. 

Structure. — In    the 
wall    of    the   trachea 

there  are  from  sixteen  to  twenty  C-shaped  cartilage 
rings  that  make  a  little  more  than  two-thirds  of  a  cir- 
cle. The  outer  surface  of  these  cartilages  is  flat,  but 
the  inner  surface  is  convex  from  above  downward,  so 
as  to  give  greater  thickness  in  the  middle  than  at  the 
edges.  The  cartilage  is  of  the  hyaline  variety  and  is 


Ciliated  epi- 
thelium. 

Longitudinal 
elastic  fbers. 


^Mucous 
glands. 


Fat  cells. 


Cartilage. 


Fig.  185. — From  longitudinal  sections 
of  trachea. 


ORGANS   OF   RESPIRATION. 


241 


enclosed  in  a  periosteum.  The  cartilage  rings  are  held 
together  by  a  strong  elastic  fibrous  tissue,  which  not 
only  occupies  the  space  between  them  but  is  pro- 
longed over  their  surfaces,  so  that  each  ring  appears 
imbedded  in  this  tissue.  Each  cartilage  terminates 
abruptly  behind  by  rounded  ends,  between  which 


Stratified  cili- 
ated columnar 
epithelium. 
iif  ~~  Elastic  fibers. 
>  cut  trans- 

versely. 


&& 

'jjj^W^         -^-r~,      - 


S&3%Z?2*ff7-<- 

^m&- 

MUCOS, 


Fig.  1 86. — Transverse  section  through  human  bronchus  (Bohra  and 
Davidoff). 

stretches  a  thin  layer  of  smooth  muscle  .tissue.  This 
muscle  not  only  unites  the  ends  but  is  also  found  in 
the  intervening  space  between  the  cartilage  rings, 
along  the  posterior  wall  of  the  trachea.  Outside  of 
the  transverse  fibers  are  a  few  fasciculi  having  a  lon- 
gitudinal direction. 

The  cartilage  rings  of  the  bronchi  resemble  those 

16 


242      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

of  the  trachea  in  being  incomplete  behind.  The 
right  bronchus  has  from  six  to  eight  rings,  while  the 
left  has  from  nine  to  twelve.  The  left  bronchus  is 
longer  but  narrower. 

The  mucous  membrane  is  smooth  and  contains  a 
considerable  amount  of  lymphoid  tissue  and  many 
mucous  glands.  The  epithelial  lining  consists  of 
long  columnar  ciliated  cells,  often  very  irregular  and 
even  branched  at  their  fixed  ends.  One  or  two  rows 
of  small  irregular  cells  intervene  between  the  basal 
ends  of  the  ciliated  cells,  and  this  epithelium  is 
therefore  stratified  although  very  thin.  The  cells 
rest  upon  a  basement  membrane  through  which 
nerves  pass  to  reach  the  sensitive  epithelium.  Ex- 
ternal to  the  basement  membrane,  in  what  consti- 
tutes the  membrana  propria,  there  is  a  strong  layer 
of  longitudinal  elastic  fibers.  This  tissue  extends 
the  whole  length  of  the  air  passages,  and  gives  not 
only  great  elasticity  but  is  an  obstruction  to  invading 
bacteria.  A  vascular  submucosa,  not  very  exten- 
sive, intervenes  between  the  mucosa  and  the  carti- 
lage. In  this  may  be  found  the  bodies  of  small  race- 
mose mucous  glands,  the  largest  being  in  the  poste- 
rior wall.  The  excretory  ducts  of  these  glands  open 
on  the  inner  surface.  Lymphoid  tissue  is  present 
both  in  the  mucosa  and  the  submucosa. 

THE  LUNG. 

The  lungs  occupy  the  greater  part  of  the  chest 
cavity,  of  which  they  form  an  accurate  mould.  The 
right  lung  is  the  larger  and  has  three  lobes,  while  the 
left  has  two.  Each  lung  is  suspended  freely  in  this 


ORGANS    OF   RESPIRATION.  243 

cavity  and  is  attached  only  by  a  small  part  of  its 
flattened  or  mesial  surface  called  the  root.  The 
outer  surface  of  each  lung  is  covered  by  a  serous 
membrane,  the  visceral  pleura,  which  is  reflected 
over  the  chest  wall,  where  it  is  called  the  parietal 
pleura.  The  histology  of  the  pleura  is  identical  with 
that  of  the  peritoneum. 

Each  lobe  has  one  bronchus  which  divides  rapidly 
into  smaller  bronchi.  The  latter,  instead  of  having 
cartilage  rings,  are  supplied  with  small  cartilage 
plates.  These  plates  are  not  present  in  bronchi 
whose  diameters  are  less  than  o.  i  mm.  Mucous 
glands  are  rather  numerous  but  also  disappear  in 
bronchi  less  than  o.i  mm.  in  diameter.  These 
smaller  bronchi  differ  further  from  the  larger  ones 
in  having  a  circular  layer  of  smooth  muscle  that  in- 
tervenes between  the  cartilage  plates  and  the  mucous 
membrane.  The  contraction  of  this  muscle  reduces 
the  caliber  of  the  smaller  bronchi  and  thus  regulates 
the  amount  of  air  that  passes  to  the  lung  tissue.  In 
asthma  there  is  a  spasmodic  or  more  or  less  chronic 
contraction  of  this  muscle  tissue,  which  causes  diffi- 
culty in  breathing.  The  air  is  forced  through  the 
narrow  tubes,  and  this  brings  about  a  dilatation  of 
the  terminal  passages  and  ,a  hypertrophy  of  the 
chest  muscles,  the  latter  being  due  to  the  forced 
efforts  in  securing  sufficient  air.  Asthmatic  patients, 
therefore,  have  resonant  lungs  and  usually  an  en- 
larged chest.  The  primary  trouble  in  this  disease 
is  not  in  this  smooth  muscle  tissue,  but  seems  to 
involve  the  nervous  system  and  the  innervating 
nerves.  Smooth  muscle  is  present  in  all  the  bronchi, 


244      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


even  in  the  smallest  tubes  whose  diameters  measure 
0.2  mm. 

Structure  of  the  Lung. — The  structure  of  the 
smaller  bronchi,  which  form  a  part  of  the  lung  tis- 
sue, has  just  been  described.  Our  knowledge  of  the 
terminal  air  passages  has  recently  been  greatly  in- 
creased by  the  work  of  Dr.  Miller,  of  the  University 
of  Wisconsin,  whose  account  will  be  followed.  The 
smallest  bronchioles,  whose  diameters  are  0.2  mm., 
are  called  terminal,  or  respiratory  bronchi.  In  these 

Epithelium. 
Longitiidinal 

elastic  fibers. 
Involuntary 

muscle. 
Cartilage. 

Mucous  gland. 


Fat  cells. 

Fig.  187. — Section  from  lung  showing  portion  of  small  bronchus  and. 
adjacent  lung  tissue. 

tubes  the  character  of  the  epithelial  lining  changes. 
Patches  of  small  pavement  epithelial  cells  appear 
among  the  ciliated  cells /while  at  the  end  of  the  res- 
piratory bronchus  all  are  of  the  pavement  variety. 
At  this  point  the  tube,  slightly  dilated,  opens  into 
three  to  six  distinct  chambers  called  atria.  Each 
atrium  opens  into  a  variable  number  (2  to  5)  of 
larger  irregular  spaces  called  air  sacs,  the  walls  of 
which  have  concave  spherical  depressions  called  ai? 


ORGANS   OF   RESPIRATION.  24$ 

cells,  or  alveoli.  Simple  pavement  epithelium  lines 
the  atria  and  air  sacs,  consisting  of  two  varieties  of 
cells:  (i)  small  nucleated  elements,  and  (2)  larger 
non-nucleated  plates.  The  latter  line  the  alveoli 
and  are  applied  directly  against  the  blood  capillaries, 
while  the  nucleated  elements  intervene  at  the  free 
margin  of  the  alveoli.  Before  birth  the  air  sacs  are 
collapsed  and  all  the  pavement  epithelium  is  com- 
posed of  nucleated  cells.  With  the  first  breath  of 
air  the  air  sacs  become  distended,  not  uniformly, 
but  to  form  vesiculated  walls,  the  small  vesicles  being 
the  alveoli.  The  walls  of  the  latter  suffer  greater 
distention,  due  to  a  less  resistance  offered  by  the 
opposing  blood  capillaries,  and  the  nucleated  cells  in 
this  region  become  changed  to  non-nucleated  plates, 
through  which  an  exchange  of  gases  takes  place  dur- 
ing the  functional  activity  of  the  lung.  The  atria 
and  air  sacs  vary  in  size  according  to  their  distention 
with  air.  An  average  diameter  is  i.omm.  for  the 
atria,  and  i.o  by  1.5  mm.  for  the  air  sacs.  Each  air 
sac  has  from  six  to  eight  air  cells,  or  alveoli,  that  also 
•vary  greatly  in  size,  an  average  diameter  being  0.25 
mm.  One  system  of  atria  and  air  sacs  constitute  a 
lobule  and  is  separated  from  adjacent  lobules  by  in- 
tervening areolar  tissue.  The  base  of  each  lobule  is 
directed  toward  the  surface  of  the  lung  and  the  apex 
towards  its  root.  These  lobules  can  be  seen  in  a 
macroscopic  surface  examination  of  the  lung. 

The  elastic  fibers  of  the  membrana  propria,  de- 
scribed in  the  wall  of  the  trachea  and  bronchi,  ex- 
tend to  the  distal  end  of  the  air  passages,  where  they 
spread  out  to  form  a  thin  reticular  fabric  just  ex- 


Respiratory 
bronchiole. 


Alveolar 
duct. 


Fig.  189. 

Figs.  1 88  and  189. — Two  sections  of  cat's  lung  (Bohm  and  Davidoff) 


ORGANS   OF   RESPIRATION. 


247 


ternal  to  the  pavement  epithelium,  giving  great 
elasticity  to  the  air  sacs  and  functions  in  the  expul- 
sion of  air  during  normal  breathing.  The  term  in- 
fundibulum  is  sometimes  applied  to  the  distal  air 
passage  lined  by  pavement  epithelium. 

The  following  is  a  resume  of  the  tissues  found  in 
the  walls  of  the  respiratory  passages : 


Non-nucleated 
epithelial  cell. 

Nucleated  ebi- 
'     thelial  cell. 


Fig.  190. — Inner  surface  of  human  alveolus  treated  with  silver  nitrate, 
showing  respiratory  epithelium  (after  Kolliker). 


1.  Epithelium  extends  the  whole  length.     In  the 
trachea  and  bronchi  this  is  stratified  ciliated.     In  the 
atrium  and  air  sacs  it  is  simple  pavement  and  made 
up  of  two  kinds  of  cells,  namely,  nucleated  and  non- 
nucleated. 

2.  Elastic  fibers  extend  the  whole  length.     In  the 
respiratory  parts  the  fibers  form  a  reticulum  just 


248     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


external  to  the  pavement  epithelium  and  give  elas- 
ticity to  the  lung  tissue. 

3.  Mucous  glands  are  found  in  the  walls  of  the  large 
passages  down  to  tubes  i  .o  mm.  in  diameter. 

4.  Cartilage  is  found  in  the  trachea  and  bronchi 
down  to  tubes  i.o  mm.  in  diameter.     In  the  trachea 
and  larger  bronchi  the  cartilage  forms    C-shaped 

rings,  while  in  the 
smaller  tubes  the  car- 
tilage appears  in 
plates. 

5.  Smooth  muscle  is 
found  in  the  larger 
passages  down  to 
tubes  0.2  mm.  in  di- 
ameter, or  down  to 
the  respiratory  parts. 
In  the  trachea  and  the 
larger  bronchi  this 
muscle  is  placed  in  the 
posterior  wall  and  be- 
tween the  ends  of  the 
cartilage  rings.  In 
the  smaller  bronchi  it  forms  a  circular  layer  between 
the  lining  epithelium  and  the  cartilage  plates. 

Blood  Supply. — The  lungs,  like  the  liver,  receive 
blood  from  two  sources,  arterial  blood  through  the 
bronchial  vessels,  and  venous  blood  through  the  pul- 
monary artery.  The  bronchial  arteries,  from  one  to 
three  for  each  lung,  are  much  smaller  than  the  pul- 
monary vessels,  and  carry  blood  for  the  nutrition  of 
the  lung.  They  arise  from  the  aorta  or  from  an 


Fig.  191. — Scheme  of  lung  lobule 
(after  Miller):  b.  r.,  respiratory 
bronchiole;  d.  al.,  alveolar  duct  (ter- 
minal bronchus);  a,  a,  a,  atria;  s.  al., 
air  sacs;  a.  p.,  air-cells  or  alveoli. 


ORGANS    OF   RESPIRATION. 


249 


I 

/ 


intercostal  artery  arid  follow  the  bronchial  tubes 
through  the  lung,  to  be  ultimately  distributed  in 
three  ways:  i.  They  supply  the  bronchial  lymph 
glands,  the  coats  of  the  large  blood-vessels,  and  the 
walls  of  the  bronchial  tubes,  forming  in  the  latter 
an  outer  and  an  inner  plexus  for  the  irrigation  of  the 
muscle  coat  and  the  mucous  membrane.  2.  They 
supply  the  interlobular  areo- 
lar  tissue;  and  3,  They  spread 
out  over  the  surface  of  the  lung 
beneath  the  pleura.  The 
bronchial  veins  do  not  have  so 
extensive  a  distribution  be 
cause  some  of  the  blood  sup- 
plied by  the  bronchial  arteries 
returns  by  the  pulmonary 
veins.  The  superficial  and 
deep  set  of  bronchial  veins 
unite  at  the  root  of  the  lung 
to  drain  on  the  right  side  into 
the  large  azygos  and  on  the 
left  into  the  left  upper  azygos 
vein. 

The  pulmonary  artery, 
which  supplies  the  venous 
blood,  is  a  very  large  vessel 
that  gives  branches  to  each 

lobe  of  the  two  lungs.  The  relation  of  the  pul- 
monary artery  to  the  bronchi  is  different  on  the  two 
sides.  On  the  right  side  the  first  branch  of  the  pul- 
monary artery  turns  backward  below  the  bronchus 
of  the  upper  lobe,  and  then  passes  along  the  posterior 


A 


Fig.  192.  —  Reconstruc- 
tion in  wax  of  a  single  atri- 
um and  air  sac  with  the 
alveoli:  V,  Surface  where 
atrium  was  cut  from  alveolar 
duct;  P,  cut  surface,  where 
another  air  sac  was  re- 
moved; A,  atrium;  S,  air 
sac  with  air  cells  (alveoli) 
(after  Miller). 


25°      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


surface  of  this  bronchus.  On  the  left  side  the  corre- 
sponding artery  turns  backward  above  the  level  of 
the  first  bronchial  branch.  The  bronchus  to  the 
upper  lobe  of  the  right  lung  is  therefore  called  an 
eparterial  bronchus.  All  the  other  bronchi  are  be- 
low their  respective  arteries  and  are  called  hyparterial 
bronchi.  Because  of  these  relations  it  is  believed 
that  the  upper  lobe  of  the  right  lung  has  no  homo- 
logue  on  the  left  side,  and  that  the  middle  lobe  on 
the  right  side  is  homologous  to  the  upper  lobe  on  the 

left.  The  pulmonary  ar- 
tery divides  with  the 
bronchi  and  closely  ac- 
companies them  along 
their  posterior  or  superior 
walls.  The  correspond- 
ing veins  pass  along  the 
anterior  or  inferior  walls. 
These  blood-vessels  are 
very  large,  often  as  large 
as  the  bronchial  tubes, 
but  in  no  case  do  they 
supply  blood  to  the  walls 
apex  of  the  pulmonary 
lobule,  the  pulmonary  artery  breaks  up  into  several 
small  twigs,  one  for  each  antrum,  supplying  blood 
to  an  extensive  capillary  plexus  that  spreads  over 
the  surface  of  atria  and  air  sacs.  The  capillary 
meshes  are  very  dense,  and  the  capillary  tubes  very 
large,  so  that  the  intervening  spaces  are  barely  wider 
than  the  capillaries  themselves.  Because  of  thelarge 
size  of  the  lung  capillaries  it  is  possible  for  fine 


Fig.  193. — Section  from  in- 
jected lung  showing  capillaries  of 
an  air  sac. 


of  the  bronchi.      At  the 


ORGANS   OF  RESPIRATION.  2gl 

shreds  from  a  blood  clot,  or  emboli  in  the  blood,  to 
filter  through  and  reach  the  left  side  of  the  heart  by 
the  pulmonary  veins.  If  so,  these  emboli  are 
quickly  carried  by  the  blood  current  around  the 
aorta  and  up  the  right  carotid,  as  the  latter  is  the 
most  direct  route.  This  course  takes  them  to  the 
right  side  of  the  brain,  in  which  the  capillaries  are 
narrow,  and  where  the  emboli  lodge  often  with  fatal 
results.  Such  emboli  or  shreds  of  blood  clots  pri- 
marily enter  the  venous  system  at  the  seat  of  a  bone 
fracture,  or  in  the  walls  of  the  uterus  after  parturi- 
tion, or  from  clots  of  blood  anywhere  in  the  system. 

The  pulmonary  veins  carry  blood  from  the  pul- 
monary capillary  plexus.  Each  venous  radicle 
drains  an  area  corresponding  to  several  air  cells  or 
alveoli.  At  first  these  small  veins  take  an  inde- 
pendent course  in  the  interlobular  tissue,  but  after 
they  have  attained  a  certain  size  they  accompany 
the  arteries  and  the  bronchi,  and,  as  a  rule,  along  the 
lower  and  front  aspect  of  the  latter.  At  the  root  of 
the  lung  there  are  formed  two  pulmonary  veins  on 
each  side  which  open  separately  into  the  left  auricle. 
The  pulmonary  veins  have  no  valves,  and  unlike  the 
veins  of  other  organs  are  more  capacious  than  their 
corresponding  arteries. 

Lymphatics. — The  lymphatics  of  the  lung  are  very 
extensive  and  accompany  the  two  blood  systems. 
We  may  therefore  divide  them  into  two  sets,  a 
bronchial  and  an  alveolar.  The  bronchial  consists  of 
an  elaborate,  fine  plexus  that  ramifies  through  the 
mucosa  and  submucosa  of  the  bronchial  tubes.  This 
set  anastomoses  freely  with  a  second  plexus  just  ex- 


252      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

ternal  to  the  smooth  circular  muscle  layer  of  the 
bronchi.     Lymph    nodes    are    interpolated    ever} 
where  in  these  plexuses.     Just  beneath  the  pleur 
all  over  the  surface  of  the  lung,  lymphatics  ramii^ 
and  drain  toward  the  root  of  the  lung,  where  they 
join  the  lymphatics  located  in  the  bronchial  walls. 

The  alveolar  set  accompany  the  pulmonary  vessel 
These  lymphatics  have  their  origin  in  a  plexus  tha 
surrounds  the  respiratory  or  alveolar  portions  of  the 
lungs,  and  then  accompanies  the  pulmonary  arteries 
and  veins  along  the  external  surfaces  of  the  bronchial 
tubes  to  the  root  of  the  lungs,  where  they  ultimately 
unite  with  the  bronchial  lymphatics.  While  lym- 
phatic nodes  are  present  everywhere,  they  are  par- 
ticularly abundant  at  the  root  of  the  lung.  As 
tuberculosis  spreads  along  the  lymphatics,  the  dif- 
ferent clinical  aspects  of  this  disease  depend  to  a 
considerable  extent  on  which  of  these  systems  be- 
comes involved. 

Nerves. — The  nerves  of  the  lung  come  from  the 
pneumogastric  and  the  sympathetic,  and  are  made 
up  of  medullated  and  non-medullated  fibers.  They 
enter  at  the  root  of  the  lung  and  accompany  the 
blood-vessels  to  the  terminal  air  passages,  where 
they  arborize  about  the  lung  alveoli  just  external  to 
the  epithelial  lining.  Many  nerve  ganglia  are  located 
along  their  course  and  many  fine  fibers  are  given  off 
that  innervate  the  musculature  and  epithelial  lining 
of  the  bronchial  tubes  and  the  walls  of  the  blood^ 
vessels. 


CHAPTER  VII. 
THE  URINARY  ORGANS. 

r  The  following  organs  will  be  considered  under  this 
topic:  Suprarenal  glands,  Kidney,  Ureter,  and  Blad- 
der. The  urethra  will  be  described  in  connection 
with  the  generative  organs. 

THE  SUPRARENAL  GLANDS. 

The  suprarenals,  morphologically,  belong  to  the 
nervous  system,  but  their  close  proximity  to  the 
kidneys  makes  it  advisable  to  describe  them  here. 
They  are  two  triangular  flattened  organs  covered 
with  fat  that  lie  one  on  either  side  of  the  spine,  in 
close  proximity  to  the  upper  kidney  border.  The  left 
one  is  slightly  larger  and  measures  from  one  and 
one-fourth  to  one  and  one-half  inches  from  above 
downward,  one  and  one-fourth  inches  from  side  to 
side,  and  one-sixth  to  one-eighth  inch  in  thickness. 

Embryologically,  the  organs  consist  of  a  cortical 
part  that  develops  in  connection  with  the  Wolffian 
body  and  therefore  comes  from  the  mesoderm,  and  a 
medulla  which  is  associated  with  the  sympathetic 
nervous  system  and  is  derived,  at  least  in  part,  from 
the  ectoderm.  The  medulla  decomposes  very  rapid- 
ly after  death,  and  the  organ  then  resembles  a  cap- 
sule; hence  the  name,  suprarenal  capsule,  is  often 
used. 

253 


2$4      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


Each  suprarenal  is  invested  in  a  fibrous  capsule  and 
a  liberal  supply  of  fat.  The  capsule  contains  many 
elastic  fibers  and  some  smooth  muscle  cells. 

The  cortex  shows  a  radial  structure  and  has  been 
divided  into  three  zones,  which  are  not  very  well  de- 
fined. 

i.  The  zona  glomerulosa,  next  to  the  capsule,  con- 
sists of  a  row  of  columnar  epithelial  cells  folded  in 
such  a  way  as  to  form  oval  bodies  or  elongated  heads 
separated  by  strands  of  connective  tissue  from  the  cap- 
sule. The  oval  nuclei  are  in  the  middle  of  the  cells. 

2.  The  zona 
fasciculata  makes 
up  the  larger  por- 
tion  of  the  cortex 
and  consists  of 
anastomosing  col- 
umns of  epithelial 
cells,  a  continua- 


C  or  lex. 


Httum. 


Fig.  194. — Cross  section  of  suprarenal  gland 
of  man. 


Blood-vessels. 

tion  of  the  zona 
glo  merulo  sa. 
Each  column  has  two  rows  of  polygonal  cells  that  are 
smaller  than  those  of  the  glomerulae. 

3.  The  zona  reticularis  borders  on  the  medulla. 
Here  the  columns  anastomose  and  freely  interlace. 
The  cells  resemble  those  of  the  fasciculata.  Con- 
nective tissue  ramify  between  the  columns,  hence 
the  radial  appearance  of  the  cortex. 

The  medulla  is  coarsely  vascular.  The  cells  are 
smaller  than  those  of  the  cortex  and  are  grouped  in 
round  or  oval  masses.  These  cells  are  finely  gran- 
ular, often  pigmented,  and  stain  a  brown  color, 


PLATE  IV. 

DIAGRAMMATIC  REPRESENTATION  OF  THE  DEVELOPMENT  OF  THE  GENITO- 
URINARY SYSTEM,   THE  WOLFFIAN  BODY  AND   ITS  DERIVATIVES 
BEING  COLORED  RED,  THE  MULLERIAN  DUCT  AND  ITS  DERIVATIVES, 
GREEN  (Heisler): 
i,  Indifferent  type;  2,  indifferent  type,  later  stage,  the  Wolman  and 

Miillerian  ducts  and  the  primitive  ureter  now  opening  into  the  urogenital 

sinus;  3,  male  type,  lower  ends  of  Miillerian  ducts  fused  to  form  the  sinus 

pocularis;  4,  female  type. 


PLATE 


THE  URINARY  ORGANS. 


2S5 


Numerous  ganglion  cells  are  present  and  many  nerve 
fibers. 

Blood-vessels. — Each  suprarenal  gland  receives 
three  arteries, — one  each  from  the  aorta,  the  phrenic, 
and  the  renal.  The  arteries  break  up  into  small 
branches,  most  of  which  enter  the  medulla  through 
the  hilum.  Some  branches  ramify  in  the  capsule 


Cortex, 


.^.  .«  % 

?OT?  }  -*    Capsule. 

~£vj<  * 

>  — • «  Zona  glomerulosa. 


-*  Zona  fasciculate. 


—  Zona  relicularis. 


Medulla. 


Fig.  195. — Section  of  suprarenal  gland  of  dog. 

and  from  there  enter  the  cortex,  where  they  form 
capillaries  around  the  columns  of  epithelial  cells. 
Those  that  enter  the  medulla  form  a  coarse  plexus 
in  this  part,  and  then  send  smaller  capillaries  into  the 
cortex  to  anastomose  with  those  from  the  capsule. 
The  veins  pass  out  from  the  center,  usually  one  from 


256     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

each  organ.  The  vein  from  the  right  suprarenal 
enters  the  vena  cava,  while  that  from  the  left  empties 
into  the  renal.  Lymphatics  accompany  the  blood- 
vessels. 


Fig.  196. — Arrangement  of  the  intrinsic  blood-vessels  in  the  cortex  and 
medulla  of  the  dog's  adrenal  (Fig.  17,  Plate  V,  of  Flint's  article  in  "  Con- 
tributions to  the  Science  of  Medicine,"  dedicated  to  Professor  Welch. 
1900). 

The  nerves  are  exceedingly  numerous  and  come 
from  the  solar  and  renal  plexuses  of  the  sympathetic, 
and  medullated  fibers  from  the  phrenic  and  pneumo- 
gastric.  They  ramify  freely  among  the  ganglionic 
cells  of  the  medulla  and  between  the  cells  of  the  cor- 
tex, particularly  those  of  the  glomerulosa. 


THE   URINARY   ORGANS.  257 

The  function  of  the  suprarenal  gland  is  not  known. 
Its  extirpation  in  the  dog  is  followed  by  death  in  a 
few  days.  There  are  at  least  three  interesting  clini- 
cal features  connected  with  this  organ : 

1.  Suprarenal  extract,  taken  internally,  increases 
arterial  tension  by  contracting  the  small  arterioles. 
The  extract  has  the  same  effect  when  sprayed  upon 
surfaces,  therefore  it  is  much  used  in  nose,  throat, 
and  eye  work,  to  check  hemorrhage  and  reduce  con- 
gestion. 

2.  The  cortical  cells  may  produce  a  malignant 
growth    called    a    hypernephroma.     The    malignant 
cells   may   invade   and   replace   the   kidney.     The 
growth  usually  spreads  to  the  liver  and  adjacent  or- 
gans, causing  death  in  one  to  three  years. 

3.  Addison's  Disease  is  a  chronic,  usually  tubercu- 
lar, inflammation  of  the  suprarenal  glands,  fatal  in 
one  or  two  years.    It  is  accompanied  with  a  striking 
bronze  pigmentation  of  the  skin,  and  digestive  and  ner- 
vous disturbances.     It  is  a  rare  disease  of  middle  life. 

The  above  facts  support  the  view  that  the  organ 
secretes  a  substance  that  is  regularly  gathered  up  by 
the  blood.  This  secretion  may  control,  in  a  measure, 
arterial  pressure.  The  organ  is  also  a  relay  in  the 
sympathetic  nervous  system  which,  when  destroyed, 
as  in  Addison's  Disease,  accounts  for  the  gastric  and 
nervous  symptoms. 

THE  KIDNEYS. 

The  kidneys,  two  in  number,  are  compound  tubular 
epithelial  glands  derived,  embryologically,  from  the 
mesoderm.     They    are    situated    behind    the    peri- 
17 


258      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

toneum,  one  on  each  side  of  the  vertebral  column  and 
on  a  level  with  the  last  dorsal  and  the  upper  two  or 
three  lumbar  vertebrae.  They  are  held  in  position 
by  the  renal  vessels,  by  a  loose  areolar  tissue  that 
surrounds  them  which  contains  much  fat,  and  by 
the  abdominal  pressure.  Each  kidney  measures 
four  inches  in  length,  two  and  one-half  inches  in 
breadth,  and  one  and  one-fourth  to  one  and  one- 
half  inches  in  thickness. 

Their  developmental  history  is  rather  complex 
and  can  be  but  briefly  given  here.  It  involves  the 
history  of  the  pronephros,  mesonephros,  and  meta- 
nephros,  three  sets  of  excretory  organs  which  re- 
place each  other  in  the  sequence  in  which  they  are 
mentioned. 

1.  The  pronephros,   or  head  kidney,   develops  in 
connection  with  the  nephrotomes  of  the  first  three  or 
four  embryonic  somites.     These  nephrotomes  unite 
with    a    longitudinal    duct,    the    pronephric    duct, 
which  opens  posteriorly  into  the  cloaca.     With  this 
organ  fluid  from  the  celomic  or  peritoneal  cavity 
can  be  eliminated,  and  also  waste  products  from  the 
blood,  as  a  tuft  of  blood  capillaries  or  glomerulus 
is  present  near  the  peritoneal  opening  of  each  nephro- 
tome.     This  kidney  is  exceedingly  rudimentary  in 
mammals  and  functional  only  in  larval  stages  of 
amphibians  and  in  bony  fishes. 

2.  The  mesonephros,   or   Wolffian  body,   develops 
in   connection   with  the    nephrotomes    posterior    to 
those  that  form  the  pronephros.     The  pronephric 
duct  becomes  the  Wolffian  duct  and  drains  from  the 
peritoneal  cavity  in  the  same  manner  as  in  the  head 


THE   URINARY   ORGANS.  259 

kidney.  The  glomerulus  in  this  case  is  situated  in 
the  wall  of  the  nephrotome,  which  makes  the  meso- 
nephros  a  more  efficient  organ.  The  mesonephros 
is  an  elongated  segmented  organ  and  a  permanent 
structure  in  amphibians.  It  is  an  embryonic  organ 
in  birds  and  mammals,  in  which  it  is  replaced  by 
the  metanephros. 

3.  The  metanephros,  or  permanent  kidney,  develops 
as  a  diverticulum  from  the  cloacal  end  of  the  Wolffian 
duct.  The  diverticulum  lengthens  into  a  tube,  the 
ureter.  The  upper  or  anterior  end  of  the  tube 


Artery. 


Vein. 


Fig.  197. — Kidney  of  new-born  infant,  showing  a  distinct  separation 
into  reniculi;  natural  size.  At  a  is  seen  the  consolidation  of  two  adjacent 
reniculi  (Bohm  and  Davidoff). 

branches  to  form  a  number  of  smaller  tubes,  the  uri- 
niferous  tubules  of  the  kidney.  The  surrounding 
mesoderm  becomes  condensed  and  vascular,  inter- 
lacing between  the  tubules  to  form  the  adult  kidney. 

The  development  of  the  urinary  system  is  closely 
associated  with  that  of  the  generative  system,  and 
will  be  referred  to  again  when  the  latter  is  described. 

Structure. — The  hilus  of  the  kidney  is  an  opening 
through  which  the  ureter  and  blood-vessels  pass. 
On  making  a  longitudinal  section  of  the  kidney,  it 
will  be  seen  that  the  hilus  leads  to  an  expanded  fis- 


260     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


sure,  the  renal  sinus.  The  pelvis  is  a  funnel-shaped 
expansion  of  the  ureter  that  occupies  a  large  portion 
of  the  sinus.  The  contents  of  the  sinus  may  be  re- 
moved, when  the  exposed  wall  will  be  found  to  be 

kidney  substance. 
Each  kidney  is 
enclosed  in  a 
smooth  fibrous  cap- 
sule of  areolar  tis- 
sue, a  part  of  which 
also  lines  the  sinus. 
The  capsule  is 
finely  vascular  and 
can  easily  be  de- 
tached. If  it  ad- 
heres to  the  kidney 
substance  it  is  evi- 
dence of  disease. 

It  is  customary 
to  describe  the  kid- 
ney as  made  up  of 
two  layers,  an  out- 
er, or  the  cortex,  and 
an  inner,  the  me- 
dulla, although 
there  is  no  sharp 


Fig.  198. — Longitudinal  section 
through  the  kidney:  I,  Cortex;  i',  medul- 
lary rays;  i",  labyrinth;  2,  medulla;  2', 
papillary  portion  of  medulla;  2",  boun- 
dary layer  of  medulla;  3,  transverse  sec- 
tion of  tubules  in  the  boundary  layer;  4, 
fat  of  renal  sinus;  5,  artery;  *,  transverse 


medullary  rays;  A,  branch  of  renal  artery; 
C,  renal  calyx;  U,  ureter  (after  Tyson 
andHenle). 


line  dividing  the 
two.  The  medulla 
consists  of  ten  or 

twelve  separate  conical  masses  called  Malpighian,  or 
medullary  pyramids,  so  arranged  that  their  bases  bor- 
der on  the  cortical  layer  and  their  apices  point  toward 


THE   URINARY  ORGANS. 


261 


the  renal  sinus  where  they  form  papillae.  The 
medullary  substance  is  more  dense  than  the  cortical 
and  is  strictly  striated,  which  is  due  to  the  radiating 
course  of  the  tubules  in  this  part.  At  the  base  of 
each  Malpighian  pyramid  these  tubules  pass  up  into 
the  cortical  substance  and  are  grouped  to  form 
cone-like  masses  called  medullary  rays,  or  pyramids  of 


Capsule. 
Glomeruli. 


Pyramid  of  Ferrein. 


Fig.  199.  —  Section  through  cortex  and  medulla  of  kidney. 


Ferrein,  the  apex  of  each  being  in  close  proximity  to 
the  periphery  of  the  kidney.  There  are  thus  a  great 
many  medullary  rays  for  each  Malpighian  pyra- 
mid. The  portions  of  the  kidney  that  intervene 
between  the  medullary  rays  are  called  the  labyrinth, 
and  consist  largely  of  convoluted  tubules.  The 
cortical  substance  not  only  covers  the  bases  of  the 


262      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

Malpighian  pyramids,  but  sends  prolongations  be- 
tween them  down  to  the  renal  sinus.  These  cortical 
prolongations  are  called  the  columns  of  Bertini,  of 
which  there  are  as  many  as  there  are  Malpighian 
pyramids. 

It  is  convenient  to  describe  the  kidney  tubules  as 
consisting  of  nine  parts.  Each  tube  commences  in 
the  labyrinth  of  the  cortex  with  (i)  an  invaginated 
dilatation  called  Bowman's  capsule.  This  capsule 
is  lined  by  simple  squamous  epithelium  which, 
when  invaginated,  makes  two  layers,  the  lumen  of 
the  tube  being  between  these  layers.  Into  the  in- 
vaginated cavity  is  crowded  a  tuft  of  blood  capil- 
laries called  a  glomerulus.  A  liberal  supply  of  con- 
nective tissue  blends  with  these  capillaries.  The 
capsule  and  glomerulus  are  frequently  called  a 
Malpighian  corpuscle.  At  the  base  of  the  cap- 
sule each  tube  is  constricted,  forming  (2)  the  neckt 
after  which  it  becomes  much  convoluted  and  wide, 
forming  (3)  the  proximal  convoluted  tubule.  The 
cells  of  this  part  are  large  with  very  thin  cell 
walls.  The  cytoplasm  immediately  around  the  nu- 
cleus is  granular,  but  toward  the  basement  membrane 
it  is  striated  with  lines  at  right  angles  to  the  mem- 
brane. The  tube  now  approaches  the  medulla, 
becomes  nearly  straight,  but  rapidly  narrows  to 
form  (4)  the  spiral  portion.  It  now  passes  straight 
down  a  Malpighian  pyramid,  where  it  makes  a  short 
curve,  and  returning  thus  forms  (5)  the  loop  of 
Henle.  This  loop  has  a  narrow  descending  limb 
with  a  short  curve,  and  a  wider  ascending  limb. 
The  narrow  descending  limb  and  curve  has  simple 


THE   URINARY   ORGANS.  263 

flat  epithelium,  so  that  the  lumen  is  practically  as 


Bowman's  capsule.  Glomerulus. 


Ascending  limb  of  Henle's  loop. 


Loop. 


Collecting  tube. 


Fig.  200. — Diagram  of  kidney  tubule. 

large  as  that  of  the  preceding  part.     The  ascending 


264      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


is  larger  but  the  epithelium  takes  on  the  char- 
acteristic  of  the  proximal  convoluted  tube,  although 
the  cells  are  a  little  smaller  and  may  contain  pig- 
ment granules.  The  ascending  limb  passes  straight 
up  a  medullary  ray,  from  which  it  emerges  to  again 
enter  the  cortex,  where  it  becomes  irregular  in  out- 
line forming  (6)  the  irregular  tubule,  which  quickly 
becomes  much  twisted  and  coiled  to  form  (7)  the 
distal  convoluted  part.  In  the  irregular  part  the  cells 

are  very  un- 

Con-voluted  . 

portions,  equal  in  size 
and  a  rod- 
like  struc- 
ture of  the 
cytoplasm 
is  very  dis- 
tinct, while 
the  base- 
ment mem- 
brane is  said 
to  be  ab- 
sent. The 
cells  of  the 


Neck. 


Fig.  201. — Section  of  a  portion  of  the  labyrinth  of  the 
kidney  cortex. 


distal  convoluted  tube  are  rather  long,  with  a  distinct 
membrane  and  a  highly  refractive  appearance  of  the 
protoplasm.  Near  the  basement  membrane  minute 
projections  from  adjacent  cells  may  be  seen  to  inter- 
lock. Finally,  this  portion  terminates  in  (8)  a 
short  functional  tubule,  which  leaves  the  cortex  and 
enters  a  medullary  ray  to  join  the  last  part  (9) ,  the 
collecting  tubule.  The  latter  passes  straight  through 
the  Malpighian  pyramid  to  open  on  its  surface  in  a 
small  pore.  In  its  course  the  collecting  tube  receives 


THE   URINARY    ORGANS.  265 

not  only  other  junctional  tubules  but  also  unites 
with  other  collecting  tubes.  The  junctional  part  is 
narrow  but  its  lumen  relatively  large,  being  lined  by 
clear  flat  or  cubical  cells.  The  collecting  tubes  are 
large  and  have  a  lining  of  simple  cubical  epithelium. 
The  location  of  the  different  parts  of  the  kidney 
tubules  may  be  tabulated  as  follows : 

Portion  of  Tubule.  Location. 

1.  Bowman's  capsule cortical  labyrinth. 

2.  Neck cortical  labyrinth. 

3.  Proximal  convoluted cortical  labyrinth. 

4.  Spiral  portion medullary  rays. 

5.  Loop  of  Henle: 

(a)  Descending  limb medulla. 

(b)  Loop medulla. 

(c)  Ascending  limb medulla  and  medullary  rays. 

6.  Irregular  part cortical  labyrinth. 

7.  Distal  convoluted cortical  labyrinth. 

8.  Junctional  tubule medullary  rays. 

9.  Collecting  tubule medullary  rays  and  medulla. 

It  will  be  observed  that  the  walls  of  these  tubules 
consist  of  simple  epithelium ;  that  this  is  made  up  of 
pavement  cells  in  the  capsule,  neck,  and  descending 
limb  of  Henle 's  loop ;  while  large  cubical  or  columnar 
cells  with  granular  and  rod-like  structure  of  the  cyto- 
plasm are  found  in  the  convoluted  parts  and  ascend- 
ing limb  of  Henle 's  loop;  and  a  low  cubical  epithe- 
lium invests  the  junctional  and  collecting  tubules. 

Casts. — It  is  common  in  high  fevers  and  in  diseases 
of  the  kidney  to  find  moulds  of  the  uriniferous 
tubules  in  the  urine.  In  high  fevers  blood  may 
enter  and  congeal  in  the  uriniferous  tubules,  the 
kidney  secretion  forces  out  this  obstruction,  which 
then  appears  in  the  urine  as  a  blood  cast.  A  clear 
serum  mould  is  called  a  hyaline  cast.  In  more 
chronic  cases  the  cells  of  the  tubules  are  carried  away 


266 


NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 


and  the  mould  is  then  called  an  epithelial  cast.  The 
cells  may  have  decomposed,  when  it  becomes  a 
granular  cast.  Hyaline  casts  often  show  granula- 
tions and  are  then  also  called  granular  casts.  Finally, 
fatty  degenerations  may  appear  and  form  fatty 
casts.  The  recognition  and  identification  of  casts 
form  an  important  subject  in  clinical  analysis.  If 
small  pieces  of  kidney  are  treated  with  strong  hydro- 
chloric acid  and  the  detritus  thus  produced  be  ex- 
amined in  gly- 
cerin, under  a  low 
magnification, 
many  pieces  of 
the  uriniferous 
tubules  are  read- 
ily observed. 
These  pieces  are 
practically  iden- 
tical with  the  epi- 
thelial and  gran- 
ular casts  of  the 
diseased  kidney. 
Blood-vessels. — The  kidneys  are  highly  vascular 
and  receive  a  large  amount  of  blood  in  proportion  to 
their  size.  The  renal  artery  and  renal  vein  pass 
through  the  hilum,  the  artery  between  the  vein  and 
ureter.  In  the  renal  fissure  the  artery  breaks  up 
into  four  or  five  branches  which  lie  external  to  the 
pelvis  of  the  ureter.  These  branches  pass  directly 
to  the  columns  of  Bertini,  where  they  break  up  into 
smaller  vessels  and  rise  to  the  level  of  the  Mal- 
pighian  pyramids.  At  this  level  they  pass  across 
the  pyramids,  between  the  latter  and  the  cortex, 


Capillary. 


Fig.  202. — Section  of  a  portion  of  a  kidney 
medulla. 


URINARY   ORGANS. 


267 


Stellate  vein. 


forming  what  are  called  arterial  arches.  The  ar- 
teries form  incomplete  arches  across  the  base  of  the 
pyramid,  while  the  accompanying  veins,  in  this 
place,  form  complete  venous  arches  across  the  base 
of  the  pyramid.  From  the  arches  interlobular 
arteries  pass 
outward  be- 
tween the  me- 
dullary rays 
and  among  the 
convoluted  tu- 
bules, taking  a 
direct  course 
toward  the  sur- 
face of  the  kid- 
ney. At  inter- 
vals they  give 
off  curved  short 
branches  which 
pass  directly  to 
the  glomerulus 
of  a  Malpig- 
hian  corpuscle, 
where  they 
break  up  into 
a  spongy  mass 
o  f  capillaries. 
A  vein,  smaller 
than  the  artery, 
emerges  from 
the  glomerulus 
close  to  the 
point  where  the  artery  enters. 


Capsule. 


Interlobular 
artery. 


Vas  afferens. 
Vas  efferens. 


Glomerulus. 


Arterial  arch 
between  the 
cortex  and 
medulla. 

Pseudo-arteria 
recta. 


Arteria  recta. 


203. — Diagram  of  blood  supply  of  kidney. 


The  artery  is  called 


268      NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 

the  vas  afferens  and  the  smaller  vein  the  vas  efferens. 
The  latter,  instead  of  uniting  with  other  veins  to  form 
larger  trunks,  as  is  the  case  in  other  organs,  passes 
directly  to  the  convoluted  tubules,  where  it  forms 
a  dense  capillary  system  that  ramifies  everywhere 
over  the  walls  of  these  tubules.  Many  of  the  effer- 
ent vessels  from  the  lowermost  glomeruli,  that  is, 
those  nearest  the  medulla,  break  up  into  pencils  of 
straight  vessels  called  pseudo-arteries  recta,  which 
pass  directly  into  the  medulla  to  form  capillaries 
around  the  tubules  of  this  part. 

Interlobular  veins  convey  the  blood  from  the  kid- 
ney cortex  to  the  venous  arches  at  the  base  of  the 
pyramids.  Near  the  periphery  of  the  kidney  other 
veins  converge  to  form  a  stellate  appearance  just 
beneath  the  capsule.  These  stellate  veins  receive 
blood  from  the  venous  arches  and  also  connect  with 
the  veins  of  the  capsule. 

The  blood  supply  of  the  medulla  is  to  a  great  ex- 
tent independent  of  that  to  the  cortex,  excepting  that 
supplied  by  the  false  arteriae  rectae.  Branches  from 
the  concave  side  of  the  arterial  arches  pass  directly 
into  the  medulla,  where  they  form  bunches  of  pencils 
of  small  parallel  vessels,  the  arteries  rectcz,  which  sup- 
ply blood  to  the  walls  of  the  uriniferous  tubules  of 
this  part.  Veins  return  this  blood  to  the  venous 
arches  that  lie  between  the  cortex  and  medulla. 
These  arches  form  veins  that  pass  through  the  col-, 
umns  of  Bertini  and  ultimately  drain  into  the  renal 
vein,  which  passes  through  the  hilum  to  join  the 
inferior  vena  cava. 

On  account  of  this  extensive  blood  supply  any 
renal  disturbance  is,  as  a  rule,  accompanied  by  a  cor- 


THE   URINARY    ORGANS.  269 

responding  circulatory  disturbance.  Conversely,  a 
disturbed  circulation  or  an  enlarged  heart  is  indica- 
tive of  a  possible  nephritis. 

Nerves. — The  nerve  supply  is  derived  from  the 
cerebrospinal  system  and  the  sympathetic.  Many 
of  these  supply  the  blood-vessels,  which  they  always 
accompany,  but  some  arborize  among  the  renal 
tubules,  particularly  those  of  the  renal  cortex. 

THE  URETERS. 

The  ureters  are  two  muscular  tubes  that  conduct 
the  urine  from  the  kidneys  to  the  bladder.  The 
dilated  commencement  of  each  ureter  is  called  the 
pelvis  and  lies  with  its  base  in  the  renal  fissure,  and 
extends  through  the  hilum  to  the  lower  portion  of 
the  kidney  where  the  ureter  proper  begins.  Lateral 
expansions  of  this  pelvis  extend  to  and  enclose  the 
papillae  of  the  Malpighian  pyramids,  on  the  surface 
of  which  the  collecting  tubules  open.  These  ex- 
pansions are  called  calyces. 

The  ureters  measure  from  fourteen  to  sixteen 
inches  in  length,  and  one-fourth  inch  in  diameter. 
Each  ureter  lies  behind  the  peritoneum  and  passes 
downward  and  inward  to  the  brim  of  the  pelvis,  and 
then  forward  and  inward  to  the  base  of  the  bladder. 
The  ureters  are  about  two  inches  apart  as  they  enter 
the  wall  of  the  bladder,  through  which  they  pass 
obliquely  for  three-fourths  inch  to  open  on  the 
inner  surface  in  two  narrow  and  slit-like  openings. 
The  oblique  passage  through  the  bladder  wall  acts 
as  a  valve  to  prevent  a  return  flow  of  urine. 

Structure.— The  walls  of  the  ureter  consist  of  an 


270     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


Stratified 
epithe- 
lium. 

Mucous 
layer. 


outer  fibrous,  a  middle  muscular,  and  an  inner  mucous 
layer.  The  latter  has  many  longitudinal  folds  and 
is  lined  by  transitional  epithelium  of  four  or  five 
layers  of  cells.  The  superficial  cells  are  flat,  or  low 
cubical,  and  may  contain  two  nuclei.  Their  lower 
surfaces  have  depressions  that  fit  upon  the  rounded 
ends  of  the  second  layer,  which  consists  of  oval  or 
pear-shaped  cells.  Between  the  apices  of  the  latter 
are  two  or  three  rows  of  small,  irregular  interstitial 

cells.  Mucous 
glands  have 
been  described 
in  the  renal  pel- 
vis and  so  have 
lymphoid  nod- 
ules, but  the 
presence  of 
glands  in  the 
ureter  of  man 
is  doubtful. 
The  membrana 
propria  is  com- 
posed of  areolar 
tissue  which 
becomes  gradually  loose  toward  the  muscularis .  This 
membrane  is  like  others  of  its  kind,  having  a  limited 
blood  supply.  The  muscular  coat  is  composed  of 
smooth  muscle  cells  and  consists  chiefly  of  a  circular 
layer  between  two  thin  longitudinal  layers,  particu- 
larly well  defined  in  the  lower  part  of  the  ureter. 
The  fibrous  coat  is  relatively  thick  and  strong,  con- 
tributing fibrous  elements  that  interlace  the  muscle 
tissue. 


Fibrous 
coat. 


Fig.  204. — Cross  section  of  the  ureter. 


THE   URINARY   ORGANS.  271 

The  function  of  the  ureter  is  an  active  one.  A  few 
drops  of  urine  enter  the  ureter  and  are  propelled 
along  by  the  peristaltic  contraction  of  its  muscula- 
ture, which  forces  the  urine  in  intermittent  jets  into 
the  bladder.  In  case  of  overdistention  the  force  ex- 
erted by  this  mechanism  is  sufficient  to  rupture  the 
bladder.  In  case  of  an  obstruction  in  the  ureter, 
as  in  the  passage  of  calculi,  a  violent  contraction  of 
the  smooth  muscle  follows,  accompanied  by  severe 
pains.  In  surgical  operations  ureters  have  been 
sewed  into  the  upper  end  of  the  bladder,  or  even  into 
the  intestine.  In  the  latter  case  the  kidney  usually 
becomes  infected  with  bacteria  from  the  bowel. 

THE  URINARY  BLADDER. 

The  urinary  bladder  is  a  receptacle  for  the  reten- 
tion of  urine,  with  an  average  capacity  of  one  pint, 
although  capable  of  much  greater  distention.  When 
empty  it  lies  wholly  within  the  pelvis,  but  if  dis- 
tended it  rises  into  the  abdomen.  When  moderately 
filled  it  has  a  rounded  form,  but  when  completely 
distended  it  becomes  egg-shaped,  the  larger  end, 
called  the  base  or  fundus,  being  directed  downward 
and  backward  toward  the  rectum,  and  its  smaller 
end,  the  summit,  resting  against  the  anterior  ab- 
dominal wall.  When  distended  the  peritoneum 
covers  the  bladder,  excepting  a  triangular  space  of 
two  inches  above  the  symphysis  pubis  known  as  the 
space  of  Retzius.  This  is  of  surgical  importance, 
as  the  bladder  can  be  opened  through  this  space 
without  going  through  the  peritoneum. 

The  mucous  membrane  on  the  inner  surface  of  the 


272      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


Transitional 
epithelium. 


bladder  is  loosely  attached  to  the  muscular  is,  and  is 
slightly  corrugated  or  folded  in  the  contracted  form 
of  the  organ.  At  the  lower  part  of  the  bladder  is 
found  the  orifice  leading  into  the  urethra,  and  im- 
mediately behind  this  is  a  smooth  triangular  surface 
called  the  trigone.  The  orifices  of  the  ureters  are 
found  at  the  posterior  angles  of  the  trigone,  and  in 
the  distended  bladder  are  about  one  and  one-half 
inches  apart  and  about  the  same  distance  from  the 
urethral  orifice.  When  the  bladder  is  contracted 
this  space  is  diminished.  An  exact  knowledge  of 

these  relations 
is  important  in 
any  attempt  to 
pass  a  catheter 
into  the  ureter. 
Histology  o  f 
the  Bladder- 
There  is  a  mu  - 
cous,  submu- 
cous,  muscular, 

and  serous  coat  to  the  bladder.  The  mucous  mem- 
brane resembles  that  of  the  ureters,  with  which  it  is 
continuous.  It  is  covered  with  a  transitional  epithe- 
lium whose  cells  vary  according  to  the  distention  of 
the  bladder.  As  a  rule,  epithelial  cells  have  but  very 
little  elasticity  and  mucous  membranes,  therefore  are 
frequently  much  folded .  The  bladder  cells  are  capable 
of  considerable  distention,  when  they  become  very 
flat.  When  the  organ  contracts  they  accommodate 
themselves  to  this  condition  and  become  cubical.  The 
cells  of  the  surface  layer  are  squamous  and  have 


Fig.  205. — Section  through  the  mucosa  of  the 
bladder. 


THE    URINARY   ORGANS. 


273 


concave  depressions  into  which  the  rounded  ends  of 
the  second  layer  or  pear-shaped  cells  are  adjusted. 
Two  or  more  layers  of  irregular  interstitial  cells  inter- 
vene between  the  apices  of  the  pear-shaped  cells. 
The  interstitial  cells  divide  regularly  by  karyokinesis 
and  are  then  crowded  to  the  surface  to  replace  the 
superficial  cells  that  normally  exfoliate.  There  are 
no  glands  in  the  bladder,  but  solid  cell  projections 
are  sometimes  found  that  resemble  glands.  The  blad- 
der is  a  part  of  the  allantois,  a  vesicular  evagination 
of  the  hind-gut.  The  bladder  epithelium,  therefore, 

Pavement  cell. 


Pear-shaped 
cell. 


Pavement  cells. 

Interstitial  cells. 

Fig.  206. — Epithelial  cells  from  the  bladder. 


is  of  hypodermic  origin,  while  that  of  the  ureter  is 
from  the  mesoderm. 

A  vascular  submucosa  intervenes  between  the  mu- 
cosa  and  the  muscularis.  This  is  a  thin  layer  of 
areolar  tissue,  but  sufficient  to  give  the  mucosa 
apparent  elasticity  and  enable  it  to  move  upon  the 
muscularis. 

The  muscular  coat  consists  of  smooth  muscle  fibers 
which  may  be  divided  into  bundles  of  outer  longi- 
tudinal fibers,  a  middle  strong  circular  layer,  and  an 
imperfect  inner  longitudinal  or  diagonal  stratum. 

18 


274      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

At  the  urethral  opening  the  middle  layer  is  thickened 
to  form  a  sphincter  muscle,  according  to  some  au- 
thors. The  bladder  musculature  forms  a  basket- 
work  fabric,  and  when  much  distended  intervals 
may  arise  in  its  walls  which  become  points  of  weak- 
ness through  which  the  mucosa  may  protrude,  when 
the  organ  is  said  to  be  sacculated. 

Vessels  and  Nerves. — The  bladder  is  supplied  with 
blood  from  the  superior  and  inferior  vesicle  arteries, 
and  in  the  female  also  from  branches  of  the  uterine 
artery.  The  veins  form  large  plexuses,  particularly 
around  the  neck,  sides  and  base.  They  eventually 
drain  into  the  internal  iliac.  The  nerve  supply  is 
from  the  third,  fourth,  and  sometimes  the  second 
sacral  nerves,  and  from  the  hypogastric  plexus  of  the 
sympathetic  The  latter  are  nearly  all  non-medul- 
lated. 


CHAPTER  VIII. 
REPRODUCTIVE  ORGANS  IN  THE  MALE. 

Under  this  heading  are  included  (i)  the  testes  and 
their  ducts,  (2)  epididymis,  (3)  penis,  and  (4)  pros- 
tate gland. 

THE  TESTICLES. 

The  testes  are  two  glandular  organs  for  the  produc- 
tion of  spermatozoa,  suspended  in  the  scrotum  by 
the  spermatic  cord.  Each  testicle  is  about  one  and 
one-half  inches  long,  one  and  one-fourth  inches 
wide,  and  nearly  one  inch  thick  from  side  to  side. 
The  corresponding  dimensions  of  the  ovary  are,  one 
and  one-half  by  three-fourths  by  one-half  inches. 

The  coverings  of  the  testes  are,  (i)  skin,  (2)  dartos; 
these  two  form  the  wall  of  the  scrotum.  The  skin  is 
thin  and  pigmented.  The  dartos  is  a  reddish  tissue 
continuous  with  the  two  layers  of  superficial  fascia 
of  the  groin.  It  is  vascular  and  consists  of  smooth 
areolar  tissue  and  smooth  muscle  fibers.  The  latter 
give  involuntary  contractility  to  the  scrotum  and 
produce  folds  or  rugae  in  the  skin.  (3)  Intercolum- 
nar  fascia,  which  is  a  thin  connective-tissue  layer 
closely  associated  with  (4)  .the  cremasteric  fascia. 
The  latter  is  continuous  with  the  internal  oblique 
muscle.  (5)  The  infundibuliform  fascia  comes  next 
and  is  a  continuation  downward  of  the  fascia  trans- 
versalis.  (6)  The  tunica  vaginalis  envelops  each 

275 


276     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


testicle  and  is  derived  from  the  peritoneum  during 
the  descent  of  the  organ.  It  is  therefore  a  serous 
coat  that  has  the  same  histology  as  the  peritoneum, 
and  may  be  divided  into  two  parts,  one  the  visceral 
portion  that  invests  the  surface  of  the  organ,  and  the 
other  the  parietal  portion  that  is  reflected  over  the 
surface  of  the  infundibuliform  fascia.  The  interval 
between  these  portions  constitutes  the  cavity  of  the 
tunica  vaginalis,  and  it  is  in  this  space  that  hydro- 


Tunica  vaginalis,  visceral  portion. 


Tunica  vagi- 
nalis, parie- 
tal portion. 


Tunica  albuginea. 


Epididymis. 


Vas  deferens. 


Lobule. 
Fig.  207. — Cross  section  of  human  testicle. 

cele  fluid  collects.  (7)  The  tunica  albuginea  comes 
next  and  is  a  firm  fibrous  covering.  This  tunic 
sends  fibrous  cords  or  trabeculae  into  the  testis, 
which  divide  the  organ  into  lobules.  It  is  par- 
ticularly dense  along  the  posterior  margin  of  the 
organ  where  it  also  invests  the  vas  deferens,  forming 
at  this  margin  a  mediastinum  called  the  corpus  of 
Highmore.  (8)  The  tunica  vasculosa  is  a  delicate 
vascular  layer  that  covers  the  inner  surface  of  the 


REPRODUCTIVE  ORGANS  IN  THE  MALE.    277 


tunica  albuginea.  The  three  tunics  just  mentioned 
form  the  wall  or  capsule  of  each  testicle,  and  are  so 
closely  associated  that  it  is  difficult  to  distinguish 
one  from  the  other. 

Structure. — The  testis  is  a  compound  tubular  gland 
divided  into  three  hundred  to  four  hundred  lobules. 
Each  lobule  is  conical  in  shape  with  the  apex  directed 
toward  the  mediastinum  and  the  base  toward  the 
surface  of  the  organ.  The  lobules  differ  in  size  ac- 
cording to  their 
position.  Each 
lobule  represents 
several  coiled  tu- 
bules which,  when 
unraveled,  aver- 
age two  feet  in 
length.  There 
are  at  least  six 
hundred  to  eight 
hundred  of  these 
tubules  t  o  each 
testicle.  Their 
walls  are  lined  with  stratified  epithelium  which  is  in- 
vested with  a  thin  layer  of  connective-tissue  ele- 
ments. The  epithelium  rests  upon  a  basement 
membrane  and  may  be  arranged  in  at  least  three 
irregular  groups  or  layers:  i.  A  layer  of  cubical 
cells,  with  small  nuclei,  rests  upon  the  basement 
membrane.  The  cells  of  this  layer  are  called  sper- 
matogonia.  The  columns  of  Sertoli,  or  sustentacular 
cells,  also  belong  to  this  layer.  These  columns 
are  elongated  columnar  cells  that  extend  from  the 


Spermatozoa. 

Spermatoblasts. 

Spermatocyles. 
Spermatogonia. 


Sustentacular  cell. 


Fig.  208. — Section  of  convoluted  tubules  of 
testicle. 


378      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

basement  membrane  inward  toward  the  lumen 
of  the  tube.  They  give  off  lateral  processes  that 
form  a  reticulum  about  groups  of  young  spermatozoa, 
to  which  they  give  both  support  and  sustenance, 
according  to  the  views  of  some  authors.  2.  Within 
the  first  layer  there  are  one  or  two  rows  of  large  cells 
with  large  deep -staining  nuclei.  These  are  the 
spermatocytes.  The  latter  multiply  rapidly  and 
continually  to  form,  3,  spermatoblasts  or  sper- 
matids. The  spermatids  are  small  spherical  cells 
and  each  one  in  due  time  develops  into  a  spermato- 
zoon. The  latter  ripen  regularly  in  groups  which 
seem  to  cluster  about  individual  sustentacular  cells. 
The  nucleus  of  the  spermatids  elongate  and  each 
little  spherical  cell  gradually  assumes  the  form  of  a 
mature  spermatozoon.  The  different  stages  in  this 
development  can  be  worked  out  by  a  study  of  the 
spermatids  as  seen  in  the  different  tubules.  In  the 
cross  section  of  a  single  tubule  all  the  spermatids 
will  be  in  the  same  stage  of  development.  The 
spermatozoa  when  mature  are  crowded  into  the 
lumen  of  the  convoluted  tubules,  where  they  mix 
with  a  viscid  secretion  which  probably  comes  from 
the  epithelial  wall.  The  convoluted  seminiferous 
tubules  end  blindly  near  the  surface  of  the  testis, 
where  they  are  also  said  to  anastomose  with  each 
other.  In  the  other  direction,  each  tubule  becomes 
straight  and  forms  the  tubuli  recti,  which  approach 
the  mediastinum  and  function  as  excretory  ducts. 
These  erect  tubules  anastomose  to  form  the  rete 
testis. 

Interstitial  Elements  of  the  Testis. — Like  any  other 


REPRODUCTIVE  ORGANS  IN  THE  MALE.    279 


organ  the  testicle  has  a  fine  reticulum  of  connective 
tissue  that  is  associated  with  the  capsule  or  tunica 
albuginea.  This  reticulum  consists  of  areolar  tissue 
that  not  only  intervenes  between  the  lobules,  but 
interlaces  between  the  seminiferous  tubules.  Blood 
and  lymph  vessels  are  everywhere  associated  with 
this  tissue.  In  addition  to  ordinary  connective- 
tissue  cells,  there  is  associated  with  this  reticulum 
patches  of  cells  that  re- 
semble epithelium  and 
have  yellowish  granules 
or  pigment.  These  are 
called  interstitial  cells, 
and,  like  the  areas  of 
Langerhans  of  the  pan- 
creas, are  supposed  to  se- 
crete products  regularly 
absorbed  by  the  blood. 
We  can  postulate  a  pos- 
sible function  of  these 
cells  when  we  consider 
the  function  of  the  testi- 
cle and  its  influence  on 


Fig. 


209. — Sustentacular 
cells  ~( cells  of  Sertoli)  of  the 
guinea-pig  (chrome-silver  me- 
thod) ;  profile  view:  c,  c,  Depres- 
sions in  the  sustentacular  cells 
due  to  pressure  from  the  sper- 
matogenic  cells;  d,  basilar  por- 
tion of  sustentacular  cells 
(Bohm  and  Davidoff). 

the   body    as    a    whole. 

(i)  Physiologically  the  testis  exerts  a  marked  influ- 
ence on  the  development  of  the  body.  (2)  It  is  ac- 
tively engaged  in  the  production  of  spermatozoa. 
(3)  It  is  essential  for  the  act  of  copulation. 

Early  castration  in  domestic  animals  is  a  striking 
evidence  of  the  influence  the  testicle  exerts  upon 
development.  The  change  manifest  is  both  physi- 
cal and  mental.  As  the  infantile  testis  does  not 


280      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


"  Middle  piece. 


•  Tail. 


produce  spermatozoa,  it  is  believed  that  the  secre- 
tions from  the  interstitial  cells  react  upon  the  devel- 
opment of  the  body  as  a  whole.  While  the  semi- 
niferous tubules  function  in  the  production  of  sper- 
matozoa, it  is  not  clear  that  the  accumulation  of 
semen  prompts  the  sexual  act.  For  instance,  the 
testicles  sometimes  do  not  descend  into  the  scrotum 

but  remain  in  the  body  cav- 
fry.  Frequently  such  testi- 
cles  are  of  the  infantile  type, 
that  is,  no  semen  is  devel- 
oped ;  and  yet  the  copulation 
act  in  such  males  is  not  only 
possible,  but  the  sexual  crav- 
ings may  be  actually  exagge- 
rated. The  interstitial  cells 
of  such  testicles  are  well  de- 
veloped and  the  male  is  other- 
wise normal.  Again,  the  im- 
potency  that  sometimes 
comes  with  old  age  is  said  to 
be  due  to  impaired  functional 
activity  of  the  interstitial 
cells  rather  than  to  lack  of 

spermatozoa.  We  have  no  specific  medical  treat- 
ment for  such  cases,  extracts  from  normal  testes 
having  been  tried  without  satisfactory  results. 

Spermatogenesis  and  Spermatozoa.  —  The  develop- 
ment of  spermatozoa  begins  in  man  in  early  youth 
and  usually  continues  into  old  age.  This  phenom- 
enon is  in  marked  contrast  to  ovulation  in  woman, 
where  there  is  a  cessation  or  menopause  at  about  the 


—   End  piece. 


Fig.  210. — Human  sper- 
matozoa, side  and  flat  view. 


REPRODUCTIVE  ORGANS  IN  THE  MALE.    281 

age  of  forty-five.  The  explanation  offered  to  ac- 
count for  this  difference  in  the  sexes  is  sought  in  the 
blood  supply  to  the  generative  organs.  There  is  a 
decrease  in  the  nourishment  to  the  ovaries  as  the 
menopause  approaches,  due  to  a  contraction  of  the 
blood-vessels  that  supply  the  organ.  Thetestes,  on 
the  other  hand,  have  a  liberal  supply  of  blood 
throughout  life. 

The  development  of  spermatozoa  has  been  re- 
corded with  great  accuracy,  particularly  in  ascaris, 
insects,  amphibians,  and  fishes,  and  there  is  little 
doubt  but  that  the  processes  in  mammalia  are  es- 
sentially the  same. 

The  spermatogonia  cells  of  the  testicle  after  repeated 
division  produce  what  are  called  primary  spermato- 
cytes.  Each  of  the  latter  divides  by  somatic  mito- 
sis to  produce  two  secondary  spermatocytes,  and  these 
divide  by  reduction  mitosis  to  produce  spermatids, 
which,  in  turn,  are  moulded  into  individual  sperma- 
tozoa. From  every  primary  spermatocyte,  there- 
fore, four  spermatozoa  ultimately  ripen,  a  detailed 
account  of  which  will  now  be  considered. 

Multiplication  of  spermatogonia  does  not  differ 
from  other  somatic  mitosis.  The  primary  sperma- 
tocytes,  however,  show  a  more  condensed  form  of 
chromatin,  and  while  the  usual  spireme  structures 
develop,  the  chromosomes  pair  and  fuse.  This  is  not 
a  chance  fusion,  but  is  said  to  be  a  selective  union 
called  sy  nap  sis  of  chromosomes.  This  coalition  ap- 
parently reduces  the  chromosomes  to  one-half  the 
original  number.  The  synapsis  is  usually  a  collateral 
one,  sometimes  end  to  end,  and  while  inmost  instances 
the  union  is  complete,  in  other  cases  the  double  na- 


282     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


ture  of  the  chromosomes  remains  visible.  Eachpaired 
chromosome  now  divides  not  only  by  splitting  lon- 
gitudinally, but  also  by  a  median  transverse  division, 
thus  producing  four  fragments,  each  group  of  four 
fragments  being  known  as  a  tetrad.  The  number  of 
tetrads  are  thus  equal  to  one-half  the  original  num- 
ber of  chromosomes.  The  tetrad  groups  now  ar- 
range themselves  in  the  equatorial  plane  of  the 


Four  chromosomes.   —  —  —  — f6/\V 


Primary  spermalocytes. 


Two  tetrads 


-----  Somatic  mitosis. 


Secondary  spermatocytes. 
Reduction  mitosis. 


Two  diad  groups  in , 

each  cell. 


f          I  T  I  Young  spermatozoa. 

Fig.   2ioa.  —  Diagram  of  spermatogenesis. 

spindle,  and  then  two  fragments  or  chromosomes 
from  each  tetrad  pass  to  opposite  poles  of  the 
spindle  to  form  two  daughter  cells  or  the  secondary 
spermatocytes.  The  chromosomes  of  each  daughter 
cell,  therefore,  form  in  groups  of  twos  instead  of 
fours,  and  each  group  is  now  called  a  diad.  The 
number  of  diads  is  equal  to  the  number  of  tetrads, 


REPRODUCTIVE  ORGANS  IN  THE  MALE.    283 

and  therefore  equal  to  one-half  the  original  number 
of  chromosomes.  A  new  spindle  quickly  forms  in 
the  secondary  spermatocytes,  the  diads  take  an 
equatorial  position  and  then  separate  to  form 
monads,  each  daughter  cell  or  spermatid  receiving 
an  equal  number.  The  number  of  monads  is  equal 
to  the  number  of  diad  groups  and  therefore  equal  to 
one-half  the  original  number  of  chromosomes.  The 
division  of  tetrad  groups  to  form  diads  is  usually 
considered  an  equational  or  somatic  process,  while 
the  division  of  the  diad  groups  to  form  monads  is 
looked  upon  as  a  reduction  process.  The  splitting 
of  the  tetrads  is  then  interpreted  as  a  longitudinal 
division  of  the  chromosomes,  and  that  of  the  diads 
as  an  end-to-end  division.  Each  spermatid  ulti- 
mately moulds  to  form  ripe  spermatozoa  and  thus 
every  primary  spermatocyte  produces  four  sperma- 
tozoa. 

Sex  Determination. — Cytological  and  experimental 
work  in  recent  years  have  revealed  facts  which  show 
that  certain  chromosomes  play  an  important  part  in 
the  determination  of  sex.  In  the  grasshopper  (Steno- 
bothrus  viridulus)  the  cells  of  the  male  have  seven- 
teen and  the  cells  of  the  female  eighteen  chromo- 
somes. In  case  of  the  primary  spermatocytes,  each 
with  seventeen  chromosomes,  when  synapsis  occurs, 
one  chromosome  is  left  without  a  mate.  This  odd 
one  is  called  the  accessory  chromosome,  and  can  be 
recognized  by  its  condensed  form,  heavy  staining 
qualities,  and  its  position  near  the  nuclear  mem- 
brane. When  the  primary  spermatocyte  divides, 
this  accessory  or  univalent  chromosome  remains  un- 
divided within  one  of  the  daughter  cells,  thus  mak- 


284      NORMAt   HISTOLOGY  AND   ORGANOGRAPHY. 

ing  two  kinds  of  secondary  spermatocytes.  When 
the  latter  divide  the  accessory  chromosome  also  di- 
vides, thus  giving  rise  to  two  kinds  of  spermatozoa  in 
equal  numbers,  one-half  of  them  having  eight  and 
one-half  nine  chromosomes.  The  mature  ova  have 
no  such  complications,  and  each  one  has  nine  chro- 
mosomes. When  fertilization  takes  place  two  com- 
binations are  possible.  Should  a  spermatozoon  with 
eight  chromosomes  fertilize  the  egg,  then  a  male  de- 
velops with  somatic  cells  that  have  seventeen  chro- 
mosomes, and  if  one  with  nine  is  used,  then  a  female 
is  produced  with  somatic  cells  having  eighteen 
chromosomes. 

In  some  cases  the  accessory  chromosome  has  a 
small  mate  in  synapsis.  Two  classes  of  spermatozoa 
develop,  one-half  with  a  large  and  the  other  half 
with  a  small  chromosome.  The  class  with  the  large 
chromosome  produces  females,  and  that  with  the 
small  produces  males. 

Two  kinds  of  spermatozoa,  differing  in  quality 
and  quantity  of  chromatin  material,  have  been  des- 
cribed in  the  whole  animal  phylum,  even  in  man,  and 
it  seems  to  be  proved  that  the  quality  of  the  sper- 
matozoon in  these  forms  determines  the  sex.  But 
there  are  many  forms  of  life,  particularly  in  plants, 
where  parthenogenetic  and  other  asexual  develop- 
ment prevail  and  where  sex  cycles  arise  from  fac- 
tors other  than  spermatozoa.  In  some  of  these  the 
quantity  and  quality  of  food  are  sex  factors,  while 
in  others  we  do  not  know  the  determining  agents. 

Structure  of  Spermatozoa. — A  spermatozoon  is  a 
minute  cell,  about  0.055  mm.  long  and  consisting  of 
a  nucleus  or  head,  a  middle  piece  or  body,  and  a  vibra- 


REPRODUCTIVE   ORGANS   IN   THE  MALE-          285 

tile  tail.  In  man  the  head  is  a  flattened  ovoid,  ap- 
pearing pear-shaped  or  pointed  in  one  view  and 
rounded  in  another.  It  contains  the  nucleus  and 
stains  heavily  with  nuclear  dyes.  It  measures  about 
0.0045  mm.  long,  0.0025  mm.  broad,  and  0.0015  mm. 
thick. 

The  middle  piece,  or  body,  is  cylindrical  in  man,  and 
measures  about  0.006  mm.  in  length,  and  o.ooi  mm. 
in  thickness.  In  some  animals,  as  the  rat,  a  spiral 
thread  can  be  seen  coiled  about  the  periphery, 
whilst  through  its  center  a  slender  filament  seems  to 
pass  and  be  continuous  with  the  central  filament  of 
the  tail.  This  filament  ends  in  a  terminal  enlarge- 
ment placed  in  close  proximity  to  the  nucleus  and 
known  as  the  terminal  globule. 

The  tail  is  about  0.045  mm.  long  and  tapers  toward 
the  extremity,  ending  in  an  extremely  delicate  fiber, 
the  end  piece.  Again,  in  the  rat  this  end  piece 
seems  to  be  the  terminal  part  of  the  central  filament 
of  the  middle  piece,  which  thus  extends  the  whole 
length  of  the  tail.  The  spermatozoon  is  propelled 
forward  by  a  spirally  lashing  movement  of  the  tail, 
similar  to  the  movement  of  cilia.  Movement  of 
cilia,  however,  ceases  as  soon  as  they  are  removed 
from  their  cell,  which  is  not  the  case  with  the  tail  of  a 
spermatozoon,  in  which  motion  seems  to  be  an  in- 
trinsic quality.  So  long  as  spermatozoa  remain  in 
the  male  passages  they  are  inert,  but  become  active 
as  soon  as  expelled. 

Spermatozoa  differ  a  great  deal  in  the  different 
species  of  animals.  They  are  very  hardy  cells,  and 
in  the  female  passages  may  live  for  days  and  even 
weeks.  In  some  domestic  birds,  as  turkeys,  they 


286     NORMAL-  HISTOLOGY  AND    ORGANOGRAPHY. 

live  at  least  a  month,  while  in  bats  copulation  takes 
place  in  the  fall  and  fertilization  follows  in  the  spring. 

Excretory  Ducts  of  the  Testis. — These  ducts  are 
the  tubuli  recti,  rete  testis,  vasa  efferentia,  epididy- 
mis,  and  vas  deferens. 

Tubuli  Recti. — The  seminiferous  tubules,  towards 
the  mediastinum,  unite  at  acute  angles  to  form  a 


Vas  deferens. 

Epididymis 
(globus  major). 

Vasa  efferentia. 
Tubuli  recti. 
Rete  testis. 


Epididymis 
(globus  minor). 


Fig.  211. — Diagram  of  human  testicle,  longitudinal  section. 

series  of  short  parallel  straight  tubes  called  the  tu- 
buli recti.  They  are  clothed  by  a  simple  layer  of  low 
cubical  epithelium. 

The  rete  testis  consists  of  a  reticulum  of  tubules 
formed  by  an  anastomosis  of  the  tubuli  recti  in  the 
mediastinum.  They  are  lined  by  simple  columnar 
epithelium. 

The  vasa  efferentia  are  tubules  that  lead  from  the 


REPRODUCTIVE   ORGANS  IN  THE   MALE.         287 

upper  portion  of  the  rete  testis  through  the  tunica 
albuginea  to  the  epididymis.  There  are  about  fif- 
teen of  them.  They  are  lined  by  simple  columnar 
ciliated  epithelium,  and  represent  tubules  that  em- 
bryologically  belong  to  the  mesonephros.  Outside 
of  the  epithelium  is  a  thin  investment  of  areolar 
tissue  in  which  smooth  muscle  cells  interlace. 

The  epididymis  is  a  very  much  coiled  canal,  about 
twenty  feet  long,  formed  by  the  confluence  of  the 
vasa  efferentia. 
At  the  upper 
and  posterior 
border  of  the 
testis  the  vasa 
efferentia  and 
ep  ididymis 
form  a  globular 
mass  of  tubules 
called  the  glo- 
bus  major.  At 
the  lower  and 
posterior  bor- 
der there  is  a  smaller  mass  of  coiled  tubules  formed 
by  the  epididymis,  and  called  the  globus  minor. 
The  epididymis  is  lined  by  simple  epithelium  which 
is  ciliated  in  most  places,  but  interposed  are  patches 
of  nonciliated  cells.  The  latter  form  small  areas  that 
resemble  glands.  External  to  this  epithelium  there 
is  a  thin  layer  of  smooth  muscle  fibers  which  blends 
with  vascular  areolar  tissue. 

The  va,s  deferens  begins  at  the  lower  margin  of  the 
globus  minor  and  is  a  direct   continuation  of  the 


Fig.  212. — Cross  section  of  epididymis. 


288     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 


Fibrous  coat. 

Longitudinal 

muscle. 

Circular  muscle. 


Membrana 
propria. 

Simple  epi  • 
iheliunt. 


canal  of  the  epididymis.  It  is  a  duct  about  twelve 
inches  long,  but  when  unraveled  and  extended  it  is 
eighteen  to  twenty  inches  in  length.  At  first  it  is 
rather  tortuous,  but  soon  becomes  straight  and 
ascends  along  the  inner  border  of  the  epididymis  to 
pass  directly  to  the  external  abdominal  ring,  taking 
a  vertical  course  and  forming  a  part  of  the  spermatic 
cord.  It  then  passes  through  the  inguinal  canal, 

and  reaching  the 
internal  abdomi- 
nal ring,  turns 
quickly  down- 
ward and  inward 
to  the  side  of  the 
bladder  upon 
which  it  descends, 
curving  backward 
and  downward  to 
the  neck  of  the 
bladder,  where  it 
enters  the  urethra 

Fig.  213.— Cross  section  of  vas  deferens.      through  the  pros- 

tate  gland.     In  its 

abdominal  course  it  lies  external  to  the  peritoneum, 
and  along  the  bladder  wall  it  arches  between  the 
latter  and  the  ureter.  Along  this  wall  it  becomes 
-sacculated  and  near  its  terminus  gives  off  a  lateral, 
enlarged,  and  sacculated  diverticulum,  the  seminal 
vesicle.  The  distal  end  beyond  the  opening  of  the 
seminal  vesicle,  is  a  narrow  straight  tube  called  the 
ejaculatory  duct. 

Structure. — The  wall  of  the  vas  deferens  has  three 


REPRODUCTIVE   ORGANS   IN   THE   MALE.         289 

coats,  an  inner  mucous,  a  middle  muscular,  and  an 
outer  fibrous.  The  mucous  membrane  generally 
presents  two  or  three  longitudinal  folds  and  is  lined 
with  simple  columnar  epithelium.  According  to 
some  investigators  it  may  be  ciliated  in  places  and 
even  resemble  the  transitional  epithelium  of  the 
ureters.  The  membrana  propria  resembles  that  of 
other  mucous  membranes.  No  glands  are  present. 
The  muscular  layer  is  of  the  smooth  variety.  It  con- 
sists of  a  strong  inner  circular  and  an  outer  longi- 
tudinal layer.  Near  the  epididymis  an  extremely 
thin  layer  of  longitudinal  muscle  fibers  is  present 
inside  of  the  circular  layer.  The  fibrous  layer  con- 
sists of  loose  areolar  tissue,  with  which  are  asso- 
ciated blood  and  lymph  vessels. 

Paradidymis. — This  consists  of  a  set  of  branched 
tubules  that  leads  off  as  blind  diverticulae  from  the 
canal  of  the  epididymis  or  the  vas  deferens.  There 
is  one  diverticulum  or  several  of  them.  The  length 
of  these  tubules  when  unraveled  varies  from  two  to 
twelve  inches,  and  histologically  they  resemble  the 
structure  of  the  vasa  efferentia.  Morphologically  the 
paradidymis  is  analogous  to  the  paroophoron  found 
in  the  broad  ligament  of  the  ovary,  the  origin  of 
both  being  associated  with  the  development  of  the 
tubules  of  the  mesonephros. 

Hydatid  of  Morgagni. — There  are  two  of  these 
bodies.  One  of  them,  more  constant  than  the  other, 
lies  usually  between  the  globus  major  and  the  testi- 
cle and  is  called  the  sessile  hydatid.  It  is  a  small 
cone-shaped  body  of  epithelial  cells  and  represents 
the  peritoneal  end  of  Muller's  duct,  the  analogue  of 
19 


290     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

the  fimbriated  end  of  the  Fallopian  tube  in  the 
female.  The  other  is  less  constant  and  lies  usually 
just  external  to  the  globus  major  and  is  called  the 
stalked  hydatid.  It  is  an  epithelial  body  and  repre- 
sents vestiges  of  the  peritoneal  end  of  the  pronephric 
or  Wolffian  duct.  The  stalked  hydatid  is  also 
present  in  the  female,  where  it  resembles  a  small 
cyst  closely  associated  with  one  of  the  fimbriae  of  the 
Fallopian  tube. 

The  distance  passed  by  the  spermatozoa,  before 
being  eliminated  by  the  urethra,  is  approximately 
twenty-four  feet.  The  chief  ducts  and  their  lengths 
are:  seminiferous  tubules,  each  two  feet  long;  epi- 
didymis,  twenty  feet;  and  vas  deferens,  two  feet. 
The  spermatozoa  are  themselves  perfectly  inactive 
in  making  this  passage.  During  the  copulation  act 
they  are  discharged  probably  from  the  whole  length 
of  the  vas  deferens  by  peristaltic  contraction  of  this 
duct,  and  not  only  from  the  seminal  receptacle  as 
formerly  supposed.  The  supply  of  spermatozoa 
is  extensive.  If  each  testicle  has  eight  hundred 
seminiferous  tubules,  each  two  feet  long,  then  there 
are  sixteen  hundred  feet  of  epithelial  lining  for  each 
organ  engaged  in  the  production  of  spermatozoa. 
The  semen  consists  of  a  fluid  part,  secreted  mainly 
by  accessory  reproductive  glands,  and  cell  elements 
or  spermatozoa  that  develop  in  the  testes.  In  man 
there  are  about  sixty  thousand  spermatozoa  to  each 
cubic  millimeter  of  semen. 

Vessels  and  Nerves. — The  spermatic  artery  supplies 
the  tubules  of  the  testicles  and  the  epididymis  with 
blood  directly  from  the  abdominal  aorta.  It  is  a 


REPRODUCTIVE:  ORGANS  IN  THE  MALE.       291 

long,  slender  artery  that  joins  the  spermatic  cord 
as  the  latter  passes  through  the  inguinal  canal.  As 
the  vessel  approaches  the  testicle,  it  sends  branches 
to  the  epididymis  and  then  divides  into  other 
branches  that  ramify  among  the  seminiferous 
tubules.  The  vas  deferens  receives  a  slender 
branch  from  one  of  the  vesical  arteries.  This  is 
called  the  artery  of  the  *vas  deferens,  and  reaches  as 
far  as  the  testis,  where  it  anastomoses  with  the 
spermatic  artery. 

The  spermatic  veins  begin  in  the  testis  and  epi- 
didymis and  pass  out  at  the  posterior  border  of  the 
organ,  where  they  unite  into  large  veins  that  form 
a  plexus  along  the  spermatic  cord.  Inside  the  abdo- 
men this  plexus  unites  to  form  a  single  trunk,  the 
spermatic  'vein,  which  on  the  right  side  opens  into  the 
vena  cava,  and  on  the  left  side  into  the  renal  veins. 

The  lymphatics  are  very  extensive  and  accompany 
the  veins.  They  terminate  in  the  lymphatic  glands 
which  encircle  the  large  blood-vessels  in  front  of  the 
vertebral  column. 

The  nerves  are  derived  from  the  sympathetic 
system.  There  is  a  spermatic  plexus  that  accom- 
panies the  spermatic  artery,  and  some  fibers  from  the 
hypogastric  plexus  that  accompany  the  artery  of  the 
vas  deferens. 

THE  PENIS. 

The  penis  is  a  vascular  organ  composed  principally 
of  two  corpora  cavernosa,  one  corpus  spongiosum, 
which  encloses  the  urethra,  and  the  glans,  which  is 
really  the  distal  end  of  the  corpus  spongiosum. 

The  integument  of  the  penis  is  very  thin  and  loosely 


292     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 


attached.  It  is  devoid  of  fat  and  hair  and  darker  in 
color  than  the  skin  generally.  Over  the  glans  it  is 
redoubled  in  a  loose  fold,  the  prepuce  or  foreskin. 
The  inner  layer  of  this  fold  is  attached  firmly  to  the 
base  of  the  glans  or  cervix,  and  from  there  it  becomes 
closely  adherent  to  the  glans  as  far  as  the  orifice  of 
the  urethra,  where  it  meets  the  mucous  membrane 
of  the  latter.  Over  the  glans  it  is  red,  thin,  and 
moist,  and  beset  with  numerous  large  vesicular  and 


Corpora  caver nosa. 


Prepuce. 


Dorsal  artery.      Corpora  cavernosa. 


Corpus 
spongiosum 


Urethra. 


Fig.  214. — Cross  section  of  penis:  a,  through  the  glans;  6,  through  the  body. 

nerve  papillae,  but  devoid  of  glands,  excepting 
around  the  cervix,  where  large  sebaceous  glands  are 
numerous,  called  glands  of  Tyson,  which  secrete  a 
white,  waxy,  odoriferous  substance,  the  smegma. 

The  corpora  cavernosa  are  two  parallel  cylindrical 
masses  of  erectile  tissue  that  lie  in  the  dorsum  of  the 
penis.  They  blend  together  in  the  anterior  portion, 
and  toward  the  root  of  the  penis  diverge  to  become 
firmly  attached  to  the  pubic  and  ischial  rami.  The 
anterior  extremity  of  the  corpora  cavernosa  is  cov- 
ered by  the  glans  penis. 

Structure  of  Corpora  Cavernosa. — There  is  a  median 


REPRODUCTIVE  ORGANS  IN  THE  MALE. 

fibrous  septum  between  the  two  corpora  cavernosa 
which  becomes  thin  anteriorly  and  incompletely 
separates  the  two  bodies.  There  is  an  external 
fibrous  investment,  very  strong  and  elastic.  This 
is  composed  mostly  of  longitudinal  bundles  of  white 
fibers  with  interlacing  elastic  fibers.  These  fibers 
are  intimately  associated  with  the  median  septum 
and  also  with  connective-tissue  trabeculae  that 
ramify  through  the  substance  of  the  cavernous 
bodies.  The  substance  of  the  latter  is  called  erectile 
tissue  and  is  of  a  spongy  nature.  The  trabeculae 
anastomose  and  interlace  freely  to  form  a  multitude 
of  interstices  or  cavernous  spaces.  These  are  filled 
with  venous  blood,  and  are  really  a  complex  system 
of  veins  lined  by  a  layer  of  flattened  epithelium  as 
in  other  veins.  In  the  anterior  portion  of  the  penis 
the  venous  labyrinth  of  one  corpus  cavernosum 
intercommunicates  with  that  of  the  other  through 
the  incomplete  septum.  In  the  erectile  condition 
the  corpora  cavernosa  are  distended  with  blood 
which  is  carried  away  by  two  sets  of  veins,  the  one 
set  joining  the  prostatic  plexus  and  the  pudendal 
veins,  and  the  other  draining  into  the  dorsal  vein 
of  the  penis.  The  arterial  blood  is  supplied  mainly 
by  branches  of  the  pudic  arteries,  but  the  dorsal 
artery  of  the  penis  sends  a  few  branches  through  the 
fibrous  sheath,  particularly  in  the  forepart  of  the 
organ.  The  arteries  ramify  in  the  trabeculae  and 
terminate  in  minute  capillary  branches  that  open 
into  intertrabecular  spaces.  Some  of  the  smaller 
arteries  project  into  the  spaces,  forming  peculiarly 
twisted  or  looped  vessels  called  helicine  arteries. 


294     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

The  corpus  spongiosum  is  also  composed  of  erectile 
tissue,  but  is  a  single  cylindrical  body  that  lies  below 
and  between  the  corpora  cavernosa.  Its  posterior 
extremity  is  much  enlarged  and  rounded,  and  is 
called  the  bulb.  This  lies  in  the  ventral  portion  of 
the  root  of  the  penis  just  in  front  of  the  triangular 
ligament.  Anteriorly  the  corpus  spongiosum  forms 
the  glans  penis,  which  caps  the  corpora  cavernosa. 
The  border  of  the  glans  is  rounded  and  projecting 
and  is  called  the  corona  glandis,  behind  which  is  a 
constriction  of  the  penis,  the  cervix.  In  the  whole 
of  its  extent  the  corpus  spongiosum  encloses  the 
urethra. 

Structure  of  Corpus  Spongiosum. — This  resembles 
the  erectile  tissue  of  the  corpora  cavernosa,  and  like 
the  latter  is  distended  with  blood  during  erection, 
but  is  less  rigid.  The  venous  labyrinth  is  a  finer 
meshwork  and  the  trabeculae  and  fibrous  tunic  is 
much  thinner.  In  the  glans  the  meshes  are  particu- 
larly small  and  uniform.  Plain  muscle  fibers  enclose 
the  urethra  and  also  form  a  part  of  the  external  coat. 

Urethra  in  the  Male. — The  male  urethra  extends 
from  the  bladder  to  the  end  of  the  penis,  in  length 
about  eight  and  one-half  inches.  Its  walls  are 
in  apposition,  excepting  during  the  passage  of  urine 
or  semen.  The  urethral  cleft  in  the  glans  is  vertical; 
in  the  body  of  the  penis  it  is  transverse ;  and  through 
the  prostatic  portion  near  the  bladder  it  is  crescentic. 
It  is  lined  by  a  mucous  membrane,  external  to  which 
is  a  double  layer  of  smooth  muscle  fibers,  the  inner 
fibers  disposed  longitudinally  and  the  outer  circular. 
For  descriptive  purposes  the  urethra  is  divided  into 


REPRODUCTIVE   ORGANS   IN   THE   MALE.         295 

a  prostatic  portion,   a  membranous  portion,  and  a 
spongy  or  penile  portion. 

1.  The  prostatic  portion  is  about  one  and  one- 
fourth   inches    in  length  and  passes   through   the 
prostate  gland.     This  is  the  widest  portion  of  the 
urethra  and  passes  vertically  from  the  neck  of  the 
bladder  to  the  triangular  ligament  of  the  perineum. 
In  cross  section  the  canal  is  crescentic  with  its  con- 
vexity turned  forward.     The  lining  membrane  pre- 
sents  longitudinal  folds,   and  along  the  posterior 
wall  is  a  prominent  median  ridge  which  gives  rise  to 
the  crescentic  form  of  the  urethra  when  seen  in  sec- 
tions.    This  ridge  is  called  the  crista,  or  verumon- 
tanum.     The  longitudinal  groove  on  each  side  of  the 
crista  is  called  the  prostatic  sinus,  which  is  pierced 
by  numerous  orifices  of  the  prostate  gland.     In  the 
middle  of  the  crista  is  the  orifice  of  a  blind  recess, 
and  at  the  lateral  margins  of  this  are  the  slit-like 
openings  of  the  seminal  or  ejaculatory  ducts.     The 
median  or  blind  recess  is  a  cul-de-sac  which  passes 
upward  and  backward  for  a  distance  of  one-fourth 
to  one-half  inch,  and  is  called  the  sinus  pocularis 
or  masculine  uterus.     It  represents  embryologically 
the  fused  ends  of  Miiller's  duct,  and  is  therefore  mor- 
phologically equivalent  to  the  female  uterus.     The 
epithelium  of  this  part  of  the  urethra  resembles  that 
of  the  bladder  and  is  of  the  transitional  variety.     In 
the  sinus  pocularis  it  is  said  by  some  to  be  simple 
ciliated  like  that  of  the  uterus. 

2.  The  membranous  portion  is  about  three-fourths 
inch  in  length  and  lies  between  the  two  layers  of  the 
triangular  ligament.     It  is  the  narrowest  part  of  the 


296     NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 


Opening  of  ureter. 


Prostate  gland. 
Sinus  pocularis. 

Ejaculatory  duct  orifice. 

Urethra,  membranous 

portion. 
Cowper's  gland. 

Urethra,  spongy  portion. 
Glands  of  Littre. 


Fig.   215. — Diagram  of  male  bladder  and 
urethra,  front  view. 


Ureter. 
Vas  deferens. 
Seminal  vesicle. 

Ejaculatory  duct. 
Prostate  gland. 


Cowper's  gland. 

Corpus  caverno- 
sum  (bulbus 
portion). 

Corpus  spongio- 
sum. 


Fig.  2 1 6. — Diagram  of  male  bladder  and 
urethra,  posterior  view. 


urethra,  not  more 
than  one-fifth 
inch  in  diameter, 
and  curves  so  as 
to  be  directed 
downward  and 
slightly  forward 
beneath  the  pubic 
arch.  The  epi- 
thelium in  this 
part  varies.  Por- 
tions of  it  resem- 
ble that  of  the 
bladder,  but  more 
often  it  presents 
the  appearance  of 
p  s  e  u  do-stratified 
with  two  or  three 
layers  of  nuclei. 

3.  The  spongy 
portion  is  by  far 
the  longest  and 
most  variable  in 
length  and  direc- 
tion. Its  length  is 
about  six  inches, 
and  its  entire 
course  is  in  the 
corpus  spongio- 
sum.  The  epithe- 
lial lining  near  the 
meatus  is  strati- 


REPRODUCTIVE   ORGANS   IN   THE  MAI^E.         297 

fied  squamous,  and  directly  continuous  with  the 
skin.  The  rest  of  this  portion  is  lined  by  columnar 
pseudo-stratified  epithelium  with  two  or  more  rows 
of  nuclei. 

The  whole  length  of  the  urethra,  excepting  its  distal 
end,  is  beset  with  small  racemose  mucous  glands  called 
glands  of  Littre.  These  vary  much  in  size,  some 
of  them  being  sacculated.  Most  of  them  open  in  the 
floor  of  the  urethra,  their  ducts  passing  obliquely  for- 
ward through  the  lining  membrane.  In  urethral  infec- 
tions these  glands  become  involved,  as  a  rule,  which 
increases  the  difficulty  of  eliminating  the  disease. 

The  Urethra  in  the  Female. — The  female  urethra 
is  about  one  and  one-half  inches  in  length,  and  cor- 
responds to  the  male  urethra  between  the  bladder 
and  the  opening  of  the  ejaculatory  ducts.  It  is 
directed  downward  and  forward  parallel  to  the  an- 
terior wall  of  the  vagina,  to  which  it  is  attached. 
The  transverse  diameter  of  the  closed  tube  is  about 
one-fourth  inch,  but  it  is  capable  of  great  disten- 
tion,  sufficient  to  admit  the  index  finger.  The  ex- 
ternal orifice,  or  meatus,  is  a  vertical  slit  with  prom- 
inent margins,  on  which  may  be  seen  the  orifices  of 
two  small  glands,  called  Skene's  glands.  The  latter 
are  subject  to  infection  in  urethral  disturbances  and 
often  give  rise  to  severe  irritations. 

THE  PROSTATE  GLAND. 

The  prostate  gland  is  a  muscular  as  well  as  glandu- 
lar organ  that  surrounds  the  prostatic  portion  of  the 
male  urethra.  It  atrophies  in  the  adult  after  cas- 


298     NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

tration,  and  remains  undeveloped  if  the  testicles 
are  removed  in  infancy,  which  supports  the  view 
that  it  is  an  accessory  organ  of  generation.  Its 
size  varies  considerably,  but  its  average  transverse 
or  longest  diameter  is  one  and  one-half  inches, 
its  antero-posterior  diameter  about  three  -  fourths 
inch,  and  its  vertical  diameter  one  and  one-fourth 
inches.  Since  the  urethra,  and  also  the  ejaculatory 
ducts,  pass  through  the  organ,  the  gland  on  this 
account  may  be  divided  into  three  lobes.  The 
wedge-shaped  portion  that  lies  between  these  ducts 
and  the  cervix  of  the  bladder  is  called  the  middle 

Artery.  Vein. 

Gland  epithelium. 


Prostatic  bodies. 


*t»j~77>"-j  -™-  '  Connective  tissue. 

^ £.;:><*  ^ 
Fig.  217. — Section  from  the  prostate  gland 


lobe,  and  the  rest  of  the  gland  is  spoken  of  as  the 
lateral  lobes.  It  is  the  latter  that  often  hypertrophy 
in  old  age  and  are  removed  in  prostatectomy.  The 
gland  lies  in  close  apposition  to  the  rectum,  and  with 
the  finger  in  the  latter  it  can  readily  be  palpated. 

The  prostate  is  a  compound  tubulo-alveolar  gland 
whose  ducts  open  into  the  prostate  portion  of  the 
urethra.  Smooth  muscle  fibers  not  onlv  surround  the 


REPRODUCTIVE)   ORGANS  IN   TH^   MALE.         299 

organ,  but  interlace  radially  toward  its  center,  form- 
ing a  network  in  whose  meshes  the  glandular  parts  are 
located.  Areolar  tissue  and  blood-vessels  accom- 
pany the  muscle  tissue.  The  alveoli  of  the  glands 
are  lined  by  simple  columnar  epithelium,  which 
sometimes  show  two  rows  of  nuclei.  These  alveoli 
contain  a  serous  acid  coagulum  and  usually  oval 
laminated  concretions  called  prostatic  bodies.  The 
latter  are  more  numerous  in  old  men.  The  numer- 
ous excretory  ducts  unite  to  form  twelve  to  fifteen 
collecting  tubes  which  open  into  the  urethra,  most 
of  them  into  the  prostatic  sinus.  These  ducts  are 
lined  by  simple  columnar  epithelium,  except  near 
their  terminations  where  it  is  transitional.  The 
organ  dorsal  or  in  front  of  the  urethra  is  mostly 
smooth  muscle  tissue. 

In  old  people  the  prostate  gland  frequently  hyper- 
trophies and  produces  urethral  stricture  with  reten- 
tion of  urine.  Prostatectomy  or  the  removal  of  the 
lateral  lobes,  usually  corrects  this  defect,  but  is  a 
serious  operation  on  account  of  the  commonly  feeble 
condition  of  these  patients.  Vasectomy,  a  much 
simpler  operation,  sometimes  gives  satisfactory  re- 
sults, but  is  not  to  be  relied  upon. 

Cow  per1  s  glands  are  a  pair  of  small  oval  bodies 
about  the  size  of  a  pea,  situated  in  the  space  between 
the  triangular  ligaments  and  in  close  proximity  to 
the  membranous  portion  of  the  urethra.  They  are 
compound  tubulo-alveolar  mucous  glands  lined  by 
simple  cubical  epithelium.  Their  excretory  ducts, 
one  for  each  gland,  are  one  and  one-half  inches  long 


300      NORMAL    HISTOLOGY   AND   ORGANOGRAPHY. 

and  run  forward  near  each  other  to  open  into  the 
floor  of  the  bulbous  portion  of  the  male  urethra. 

In  the  female  the  analogue  of  these  bodies  is 
called  the  glands  of  Bartholin.  They  open  into  and 
lie  in  close  apposition  to  the  female  urethra.  They 
may  be  palpated  in  the  lateral  walls  of  the  vestibule 
of  the  vagina. 


CHAPTER  IX. 
REPRODUCTIVE  ORGANS  IN  THE  FEMALE. 

Under  this  head  will  be  described  the  ovaries, 
Fallopian  tubes,  uterus,  vagina,  and  mammary 
^land. 

THE  OVARIES. 

The  ovaries  are  two  dehiscent  glandular  organs 
that  develop  from  the  mesoderm  in  close  apposition 
to  the  mesonephros.  Each  ovary  measures  about 
one  and  one-half  inches  in  length,  three-fourths 
inch  in  breadth,  and  nearly  one-half  inch  in  thickness. 
In  early  fetal  life  the  ovaries  lie  close  to  the  kidneys, 
but  later  they  pass  down  into  the  pelvis  where  they 
lie  in  close  proximity  to  the  iliac  fossa.  The  exact 
position  varies  considerably,  but  in  the  majority  of 
cases  they  will  be  found  placed  against  the  side  wall 
of  the  pelvis  with  their  long  axis  parallel  to  that  of  the 
body.  Each  ovary  is  held  in  position  by  a  suspen- 
sory ligament,  which  is  a  peritoneal  fold  that  passes 
downward  from  the  brim  of  the  pelvis  and  contains 
the  ovarian  vessels  and  nerves,  and  also  by  the  ova- 
rian ligament,  which  passes  to  the  uterus  and  is 
really  a  reduplication  of  the  broad  ligament.  The 
Fallopian  tube  partly  encircles  the  ovary  and  also 
contributes  to  its  support. 

Capsule  of  the  Ovary. — The  external  surface  of  the 

301 


302      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


ovary  is  of  a  pale  color  and  in  early  life  is  smooth  and 
even,  but  in  later  life  it  becomes  rough  and  marked 
by  pits  and  scars.  This  is  caused  by  the  rupture  of 
Graafian  follicles  and  the  expulsion  of  ova.  It  is 
covered  by  an  epithelium  which  is  continuous  with 
that  of  the  peritoneum,  but  differs  from  the  latter 


Uterus. 


Isthmus. 


Fallopian  tube. 


Ampulla. 
Parovarium 

Stalked 
hydatid. 


Labta 
minor  a. 
Ureth- 
ra} 

orifice, 
Labia 
majora. 


Fig.  218. — Diagram  of  female  genitalia. 


in  being  lined  by  cubical  cells  instead  of  the.  simple 
pavement  variety.  This  ovarian  epithelium  is  the 
germinal  epithelium  of  embryos,  from  which  the  ova 
and  the  other  epithelial  cells  of  each  Graafian  follicle 
are  derived.  The  germinal  epithelium  rests  upon  a 
rather  dense  investment  of  fibrous  tissue,  analo- 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       303 


gous  to  a  like  structure  in  the  testicle,  and  is  there- 
fore called  the  tunica  albuginea.  This  is  not  a  dis- 
tinct tunic  but  rather  a  condensed  part  of  the  ova- 
rian matrix.  It  is  not  well  defined,  and  is  difficult 
to  demonstrate  in  sections. 

The  medulla  is  practically  the  core  of  the  ovary 
and  consists  of  a  fibro-muscular  matrix  well  supplied 

Young  follicle  with  ovum. 


Primordial 


Germinal 
epithelium. 


Ovum  "with 
follicular 
epithelium. 


Fig.  219. — Section  from  ovary  of  adult  dog.  At  the  right  the  stellate 
figure  represents  a  collapsed  follicle  with  its  contents.  Below  and  at  the 
right  are  seen  the  tubules  of  the  parovarium  (copied  from  Waldeyer). 

with  blood-  and  lymph- vessels.  In  this  substance 
may  be  found  connective-tissue  cells,  connective- 
tissue  fibers  and  a  limited  supply  of  smooth  muscle 
fibers. 

The  Cortex. — Between  the  medulla  and  the  cap- 
sule is  the  cortex.  It  is  a  broad  zone,  not  well  de- 
fined, in  which  are  found  the  same  elements  as  in  the 


304      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 


medulla,  and  in  addition  Graafian  follicles  in  different 
stages  of  development,  and  in  older  ovaries  also  cor- 
pora lutea. 

Young  Graafian  Follicles.— Early  in  embryonic  life, 
when  the  ovary  is  clothed  with  the  germinal  epi- 
thelium which  later  becomes  the  epithelium  of  the 
capsule,  epithelial  buds  or  strings  of  epithelial  cells 
push  their  way  into  the  ovarian  cortex.  These  buds 
soon  lose  their  connection  with  the  germinal  epithe- 
lium and  form  little  groups  or  nests  of  cells  known  as 
young  Graafian  follicles.  In  each  follicle  one  cell 

takes  a  central  posi- 
tion  and  is  the  egg 
cell  or  ovum,  des- 
tined, under  proper 
conditions,  to  de- 
velop into  a  new  be- 
ing. The  ovum  in- 
creases rapidly  in 
size,  receiving  pro- 
tection and  possibly 

nourishment  from  the  investing  cells.  The  repro- 
ductive cells,  both  ova  and  spermatozoa,  can  thus  be 
traced  directly  from  the  germinal  epithelium,  which 
is  of  mesodermic  origin  and  closely  related  to  the 
pavement  epithelium  of  the  peritoneum. 

The  Graafian  follicles  occupy  the  cortical  layer  of 
the  ovary.  They  are  all  formed  during  embryonic 
life,  and  whatever  influence  environment  has  upon 
the  offspring,  that  influence  leaves  its  impression  not 
upon  the  origin  of  the  reproductive  cells,  but  upon 
their  later  development.  At  time  of  birth  it  is  esti- 


Germinal 
epithelium. 


Young 
Graafian 
follicle. 


Fig.  220. — Section  from  ovary  of  young 
dog. 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       305 


mated  that  there  are  thirty-five  thousand  eggs  or 
ova  to  each  ovary.  Only  a  small  number  of  these 
ripen  and  become  discharged  as  mature  eggs.  The 
extrusion  of  these  eggs  from  the  ovary  is  known  as 
ovulation,  and  in  woman  is  supposed  to  occur  during 
the  menstruation  period,  one  from  each  ovary. 
Menstruation  in  a  normal  woman  extends  generally 
over  a  period  of  thirty-two  years,  between  the  ages  of 
thirteen  and  forty-five.  If  thirteen  eggs  ovulate 
yearly  from  each  ovary,  there  will  be  a  possible  total 

Follicular  cavity. 


Ovum. 


Nucleolus. 
Nucleus.  Ovum. 


Nucleolus. 


Nucleus. 

Fig.  221. — Young  Graafian  follicles:  a,  follicle  with  one  layer  of  epithe- 
lial cells;  b,  follicle  with  two  layers  of  epithelial  cells. 


of  eight  hundred  and  thirty-two  that  may  ripen  dur- 
ing the  life  of  a  woman,  allowing  no  interruption  for 
pregnancies.  After  the  menopause,  ovulation  is 
supposed  to  cease. 

The  Ripe  Graafian  Follicle. — It  has  already  been 
stated  that  only  a  small  number  of  the  young  ova 
ripen  and  ovulate.  These  mature  in  the  following 
manner :  The  ovum  of  such  follicles  occupies  a  cen- 
tral position  where  it  accumulates  food  and  grows 
into  a  large  spherical  cell.  The  investing  epithelium 


306      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

forms  at  first  a  single  layer  of  cells.  These  remain 
small  and  multiply  rapidly,  forming  two  layers  of 
cells  between  which,  at  one  side  of  the  follicle,  a 
cavity  appears.  As  the  follicle  grows  larger  this  cav- 
ity, which  is  eccentric  in  position,  becomes  filled 
with  a  fluid  called  the  follicular  fluid.  The  ovum 
remains  attached  to  the  side  of  the  follicle  and  be- 
comes surrounded  by  several  layers  of  cells  called 
the  discus  proligerus.  The  outer  layer  also  multi- 


Theca. 


Follicular  cavity. 


Stratum  granu- 
losum. 


Discus  proligerus. 


Ovum. 
Fig.  222. — Ripe  Graafian  follicle. 

plies,  forming  eight  to  twelve  layers  of  cells  and  is 
then  called  the  stratum  granulosum,  to  which  the 
discus  proligerus  is  attached.  External  to  the 
stratum  granulosum  a  connective-tissue  envelope 
forms,  called  a  theca.  This  theca  develops  from  the 
ovarian  stroma  and  consists  of  two  layers,  an  ex- 
ternal, the  theca  fibrosa,  and  an  internal,  the  theca 
vasculosa,  the  latter  being  supplied  with  a  fine 
plexus  of  lymph-  and  blood-vessels.  The  mature 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       307 

Graafian  follicle  is  thus  a  sphere  that  measures  from 
one-twentieth  to  one-sixth  of  an  inch  in  diameter, 
and  lies  immediately  beneath  the  surface  epithelium 
of  the  ovary. 

The  manner  in  which  such  follicles  rupture  has 
been  variously  explained.     One  rational  theory  is 


Granular  layer  of 
large  Graafian 
follicle. 


%•• 

Fig.  223. — From  ovary  of  young  girl  (Bohm  and  Davidoff). 


that  the  pressure  of  the  accumulated  f ollicular  liquid 
obliterates  the  blood-vessels  in  the  theca  vasculosa 
next  to  the  ovarian  epithelium.  This  establishes  a 
point  of  least  resistance  at  this  place,  the  follicle 
ruptures,  and  the  follicular  fluid  with  the  ovum  is 
discharged  upon  the  surface  of  the  ovary,  the 


308      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

stratum  granulosum  and  most  of  the  discus  pro* 
ligerus  remaining  behind  in  the  ovary. 

The  Ovum. — The  ovum  has  already  been  men- 
tioned as  a  large  spherical  cell  with  a  large  accumu- 
lation of  food  material.  It  measures  0.2  mm.  in 
diameter  and  is  barely  visible  to  the  naked  eye. 
When  examined  under  the  microscope,  even  before 
the  rupture  of  its  follicle,  it  is  found  encircled  by  a 
clear  substance  called  the  zona  pellucida,  which  upon 
a  closer  examination  may  be  found  to  contain  trans- 
verse striations,  hence  it  has  also  been  called  zona 
radiata.  It  is  not  uncommon  for  a  few  of  the  epi- 
thelial cells  of  the  dis- 

•  Corona  radiata.  CUS     proKgerUS      tO     TC- 

ona  peiiudda.          main  attached  to  this 
Germinal  spot.          layer,   if    so  they   are 
Germinntc ieus^le  °r    called  the  corona  radi- 
ata.    The  zona  pelluci- 
da  is  a  secretion  from 
Fig.  224.— The  ovum.  the  adjoining  cells,  and 

one  theory  of  the  trans- 
verse striations  is  that  they  are  produced  by  minute 
cellular  processes  from  the  cells  that  form  the  corona 
radiata;  that  is,  the  first  row  of  epithelial  cells  in- 
vesting the  ovum.  It  is  affirmed  by  some  that  these 
processes  are  in  direct  communication  with  the  sub- 
stance of  the  ovum  and  are  the  means  by  which 
elaborated  food  material  is  contributed  to  the  latter. 
The  zona  pellucida  no  doubt  serves  to  strengthen 
the  delicate  ovum  after  its  expulsion  from  the  ovary. 
The  transverse  striae  in  this  membrane  may  serve  a 
further  purpose  as  primitive  channels  for  the  entrance 


REPRODUCTIVE   ORGANS   IN  THE   FEMALE.       309 

of  spermatozoa,  only  one  of  which  penetrates  the 
substance  of  the  ovum. 

The  substance  of  the  ovum  is  known  as  the  mtellus. 
It  is  a  soft  semifluid  substance  composed  of  cyto- 
plasm in  which  is  deposited  a  liberal  supply  of  food 
material  called  deutoplasm.  The  nucleus  of  the 


Primordial  egg-cell. 


Germinal  zone. 

Zone  of  mitotic  division. 
(The  number  of  gen- 
erations is  much  larger 
than  here  represented.) 


Zone  of  growth. 


Zone  of  maturation. 


Oocyte  I.  order.  — 
Oocyte  11.  order.  • ^^A  V     I.  P.B. 


\  f\ 

\       •       •      — 


Matured  ovum. 

^•r 

II.  P.B. 

Fig.  225. — Scheme  of  the  development  and  maturation  of  an  ascaris 
ovum  (after  Boveri):  P.  B.,  Polar  bodies.  (From  "Ergebn.  d.  Anat.  u. 
Entw.,"  Bd.-I.) 

ovum  is  called  the  germinal  'vesicle,  which  is  placed 
to  one  side  of  the  cell.  The  nucleus  is  unusually 
large,  about  0.05  mm.  in  diameter,  and  has  all  the 
characteristics  of  an  ordinary  cell  nucleus.  This 
was  first  described  by  Purkinje  in  the  ovum  of  birds 
in  1835.  There  is  a  well-defined  nuclear  membrane 


310     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

which  encloses  a  clear  nuclear  substance  in  which 
there  is  a  limited  amount  of  chromatin,  and  the  nu- 
cleus, therefore,  does  not  stain  heavily.  The  nucleo- 
lus,  on  the  other  hand,  is  very  prominent  and  is 
called  the  germinal  spot.  Not  infrequently  two 
nucleoli  may  be  found.  There  is  some  doubt  whether 
a  cell  membrane  to  the  ovum  is  present  before  fer- 

Primordial  sexual  cell. 


Spermatogonia . 
\ 


Spermatocyte  I.  order. 

Spermatocytes  II.  order. 

Spermatids. 


Zone  of  proliferation. 
(The  generations  are 
much  larger.) 


Zone  of  growth. 


Zone  of  maturation. 


Fig.   226. — Schematic  diagram  of  spermatogenesis  as  it  occurs  in 
ascaris  (after  Boveri).     ("  Ergebn.  d.  Anat.  u.  Entw., "  Bd.  I.) 


tilization.  After  fertilization  such  a  membrane 
appears  and  is  called  the  mtelline  membrane.  As  a 
rule  each  Graafian  follicle  contains  one  ovum ;  in  rare 
cases  follicles  are  found  with  two  and  even  with  three 
ova. 

When  a  Graafian  follicle  ruptures  and  an  ovum  is 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       311 

expelled,  a  great  activity  is  at  once  manifest  in  the 
ovum,  whether  it  is  fertilized  or  not.  The  nucleus, 
which  is  near  the  margin  of  the  ovum,  divides  in  a 
few  hours,  extruding  what  is  termed  the  first  polar 
body.  This  is  normal  cell  division,  or  mitosis.  A 
second  division  quickly  follows,  resulting  in  a  second 
polar  body.  Meanwhile  the  first  polar  body  may 
also  divide.  This  second  division  results  in  a  reduc- 
tion of  one-half  the  number  of  chromosomes,  and 
the  nucleus  thus  reduced  is  called  the  female  pro- 
nucleus,  which  is  now  ready  to  unite  with  the  male 
pronucleus  of  the  spermatozoon  and  complete  the 
process  of  fertilization.  The  phenomenon  manifest 
in  the  extrusion  of  the  polar  bodies  is  known  as 
maturation  of  the  ovum,  and  seems  to  be  an  attempt 
on  the  part  of  -the  ovum  to  develop  into  a  new  indi- 
vidual without  the  process  of  fertilization;  that  is, 
parthenogenetically.  If  the  ovum  is  not  fertilized,  it 
shows  no  further  activity  and  is  lost.  If  the  ovum 
is  fertilized  it  continues  to  divide  regularly  and  in  a 
short  time  develops  into  the  embryo. 

The  developmental  history  of  ova  is  full  of  interest. 
They  are  very  numerous  and  develop  so  very  early 
in  embryonic  life.  During  childhood  they  grow 
large  and  accumulate  a  liberal  storage  of  food,  while 
the  sister  epithelial  cells  that  form  the  Graafian  fol- 
licle remain  small  and  multiply  rapidly  to  form  the 
ripe  follicle.  This  latent  condition  extends  over  a 
period  of  fifteen  to  forty  years.  When  the  ripe  fol- 
licle finally  ruptures  and  the  ovum  is  eliminated,  a 
rapid  segmentation  quickly  follows  resulting  in  the 
extrusion  of  the  polar  bodies.  This  is  followed  by  a 


312      NORMAIv   HISTOLOGY   AND    ORGANOGRAPHY. 

second  passive  period,  unless  fertilization  takes 
place,  when  the  ovum  rapidly  develops  into  a  new 
being.  By  far  the  large  majority  of  the  ova  remain 
undeveloped  in  the  ovarian  cortex,  where  they  seem 
to  pass  merely  a  passive  existence.  We  have  no 
explanation  of  these  phenomena  beyond  attributing 
them  to  heredity,  the  nature  of  which  is  still  highly 
speculative. 

The  Corpora  Lutea. — A  corpus  luteum  is  the  modi- 
fied Graafian  follicle  after  its  rupture  and  discharge 


Surface  of  ovary. 
Epithelial  cells. 


Connective-tissue 
cells. 


Fig.  227. — Section  of  corpus  luteum. 

of  the  ovum.  This  follicle  remains  permanently 
in  the  cortex  of  the  ovary  as  a  scar.  When  the 
rupture  takes  place  the  follicular  cavity  fills  up  with 
an  exudate  and  an  infusion  of  blood  from  the  rup- 
tured blood-vessels.  This  coagulum  is  quickly  in- 
vaded by  white  blood-corpuscles,  connective-tissue 
cells  from  the  theca,  and  epithelial  cells  from  the 
stratum  granulosum.  The  corpus  luteum  thus  ulti- 
mately shows  a  uniform  distribution  of  epithelial 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       313 

cells  and  connective- tissue  cells.  If  the  ovum  be- 
comes fertilized  and  pregnancy  follows,  the  corpus 
luteum  continues  to  grow  until  it  becomes  many 
times  larger  than  the  original  Graafian  follicle,  causing 
a  rounded  elevation  at  that  point  on  the  surface  of 
the  ovary.  This  kind  is  called  a  true  corpus  luteum. 
On  the  other  hand,  if  the  ovum  is  not  fertilized  the 
corpus  luteum  shrinks  and  becomes  smaller  than  the 
original  follicle.  This  kind  is  called  a  false  corpus 
luteum.  The  corpus  luteum  is  at  first  well  defined 
by  the  investing  follicular  theca,  but  after  a  time  its 
limits  are  less  distinct,  so  that  as  age  advances  the 
ovarian  stroma  becomes  gradually  pervaded  with 
cells  like  those  of  the  corpora  lutea. 

THE  FALLOPIAN  TUBES. 

The  Fallopian  tubes  are  two  ducts  for  the  passage 
of  ova  from  the  ovary  to  the  uterus.  They  differ 
from  the  ducts  of  other  glandular  organs  in  being 
detached  from  the  organs  whose  secretions  they  con- 
vey. They  are  from  four  to  five  inches  long  and 
pass  almost  horizontally  outwards  from  the  fundus 
of  the  uterus.  When  they  reach  the  ovary  they 
ascend  along  the  pelvic  floor  and  nearly  encircle  each 
organ,  passing  up  the  external  and  down  the  internal 
or  mesial  margins.  Each  tube  is  enclosed  in  the  free 
margin  of  the  broad  ligament,  which  is  a  peritoneal 
fold  that  also  contains  the  round  ligament  of  the 
uterus,  the  ovary,  parovarium,  and  numerous  blood- 
and  lymph- vessels. 

For  descriptive  purposes  each  duct  is  divided  into 
an  isthmus,  an  ampulla,  a  neck,  and  a  fimbriated  ex- 


314     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

tremity.  The  isthmus  is  smooth  and  round,  about 
one  inch  in  length,  and  opens  into  the  fundus  of  the 
uterus  by  a  small  orifice  that  will  barely  admit  an 
ordinary  bristle.  It  is  a  straight  and  narrow  part  of 
the  duct,  about  2  to  3  mm.  in  diameter.  The  am- 
pulla encircles  the  ovary  and  is  at  least  twice  the  size 
of  the  isthmus.  It  is  also  less  firm  to  the  touch, 


Longitudinal 
muscle. 


Ciliated  ^ 
epithelium 


Fig.  228. — Cross  section  of  ampulla  of  Fallopian  tube. 

being  flabby  while  the  isthmus  is  cord-like.  The 
neck  is  an  annular  constriction  between  the  ampulla 
and  fimbriated  extremity,  the  latter  being  a'  funnel- 
shaped  expansion  of  the  ovarian  end  of  the  tube, 
which  terminates  in  a  number  of  irregular  processes 
called  fimbrice.  The  fimbriae  vary  considerably  in 
size  and  number.  Many  of  them  are  branched,  and 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       315 

one  is  particularly  long  and  attached  to  the  upper 
end  of  the  ovary. 

Structure. — The  Fallopian  duct  is  a  muscular  tube 
lined  the  whole  length  by  a  mucous  membrane 
clothed  with  simple  ciliated  columnar  epithelium. 
This  mucous  membrane  is  thrown  up  into  longitudi- 
nal folds  that  are  very  broad  and  numerous  in  the 
wide  portions  of  the  tube  and  in  the  narrow  portions 
less  conspicuous.  It  is  continuous  on  the  one  hand 


Longitudinal  muscle. 
Circular  muscle. 

Ciliated  epithelium. 


Fig.  229. — Cross  section  of  isthmus  of  Fallopian  tube. 

with  the  mucous  membrane  of  the  uterus,  and  at  the 
other  end  of  the  tube  with  the  serous  lining  of  the 
peritoneum,  being  one  example  of  a  direct  conti- 
nuity of  a  mucous  and  a  serous  membrane.  Glands, 
so  numerous  in  the  mucous  membrane  of  the  uterus, 
are  absent  in  the  Fallopian  tube. 

The  mucosa  rests  upon  a  thin  vascular  submucosa 
composed  of  areolar  tissue.  External  to  the  sub- 
mucosa there  is  a  muscular  coat  consisting  of  a  thick 
inner  circular  layer  and  a  thin  outer  longitudinal 


31 6     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

layer  of  smooth  muscle  fibers.  Externally  the  tube, 
is  practically  enclosed  by  the  peritoneum,  forming  a 
serous  covering. 

Embryologically,  each  Fallopian  tube  represents  a 
Mlillerian  duct,  which  is  derived  from  the  mesoderm. 
In  the  male  the  Wolffian  duct  develops  into  the  vas 
deferens.  This  duct,  which  is  rudimentary  in  the 
female,  is  called  Gartner's  duct,  and  lies  parallel  to 
the  Fallopian  tube,  between  the  latter  and  the  round 
ligament.  The  round  ligament  extends  from  the 
uterus  to  the  internal  abdominal  ring  in  nearly  the 
same  position  as  the  vas  deferens  does  in  man. 

Fertilization,  as  a  rule,  takes  place  in  the  upper 
part  of  the  Fallopian  tube.  In  cases  of  tubal  preg- 
nancy the  ovum  does  not  reach  the  uterus  but  finds 
lodgment  in  the  tube.  The  much-folded  mucous 
membrane  allows  considerable  distention,  but  ulti- 
mately the  rapidly  growing  embryo  ruptures  the 
tube,  with  serious  complications  resulting  from  in- 
ternal hemorrhage.  Usually  the  ova  pass  down  the 
tube  on  the  corresponding  side,  but  it  is  possible  for 
the  ova  from  one  ovary  to  pass  down  the  tube  of  the 
opposite  side.  Experimentally,  the  right  ovary  and 
the  left  tube  may  be  removed  in  the  dog  and  the  ani- 
mal still  become  pregnant. 

The  ovaries  have  a  marked  influence  on  the  devel- 
opment and  mentality  of  a  woman  and  their  removal, 
prior  to  the  menopause,  is  followed  by  deleterious 
results,  much  the  same  as  the  removal  of  the  testes 
in  the  male.  While  extracts  from  certain  organs, 
such  as  the  thyroid  gland  and  the  suprarenal  bodies, 
have  specific  medicinal  properties,  extracts  from  the 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       31? 

ovaries  give  no  satisfactory  results.  Its  potency  is 
manifest  only  by  the  living  organ  in  the  performance 
of  its  normal  function.  The  ovary  or  fragments  of 
it  will  readily  grow  in  other  parts  of  the  body,  and 
has  been  successfully  grafted  from  one  animal  to  an- 
other. 

The  Parovarium,  or  Epoophoron. — The  organ 
bearing  this  name  lies  in  the  broad  ligament  lateral 
to  the  ovary  and  between  the  latter  and  the  tube. 
It  consists  of  a  number  of  closed  epithelial  tubules 
which  can  usually  be  seen  by  holding  this  part  of  the 
ligament  up  against  the  light.  Embryologically 
they  represent  the  upper  portions  of  the  Wolffian 
duct  and  some  of  the  attached  tubules  of  the  meso- 
nephros,  and  correspond  to  the  vasa  efferentia  in  the 
male. 

The  paroophoron  represents  vestiges  of  tubules 
similar  to  the  parovarium,  situated  in  the  broad  liga- 
ment below  the  ovary.  They  correspond  to  the 
paradidymis  in  the  male. 

Being  lined  by  epithelial  cells,  either  of  these  or- 
gans may  develop  into  parovarian  or  paroophoron 
cysts,  the  former  being  more  common. 

THE  UTERUS. 

The  uterus,  or  womb,  is  a  hollow  muscular  organ, 
with  thick  walls,  placed  in  the  pelvic  cavity  between 
the  bladder  and  rectum.  In  case  of  pregnancy  it 
receives  and  nourishes  the  ovum  and  later  expels  the 
fetus  at  the  end  of  pregnancy.  During  gestation, 
and  also  periodically  during  menstruation,  it  is  sub- 
ject to  marked  physiological  and  structural  changes. 


318      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

It  is  therefore  an  organ  in  which  great  activity  is 
manifest  during  the  greater  part  of  adult  life. 

The  fully  developed  virgin  uterus  is  a  pear-shaped 
organ,  flattened  from  before  backward,  free  above, 


Fig.  230. — Arrangement  of  uterine  muscle,  as  seen  from  in  front  after 
removal  of  serous  coat  (Helie). 


and  connected  below  with  the  vagina,  into  which  its 
lower  extremity  projects.  Its  average  dimensions 
are,  three  inches  in  length,  two  inches  in  breadth  at 
its  upper  and  widest  part,  and  one  inch  in  thickness. 


REPRODUCTIVE  ORGANS  IN  THE  FEMALE. 

For  descriptive  purposes  it  is  divided  into  fundus, 
body,  and  neck,  or  cervix. 

The  fundus  is  the  broad  convex  upper  end  that 
lies  above  the  attachment  of  the  Fallopian  tubes.  It 
is  chiefly  this  part  that  expands  in  case  of  pregnancy. 
The  body  is  the  part  between  the  fundus  and  neck. 
This  part  tapers  downward  with  convex  sides.  The 


Fig.    231. — A,   Isolated   muscle-elements   of  the  non-pregnant  uterus; 
B,  cells  from  the  organ  shortly  after  delivery  (Sappey). 

neck,  or  cervix,  is  about  one  inch  long,  cylindrical, 
and  projects  into  the  anterior  part  of  the  upper  end 
of  the  vagina.  The  projecting  portion  is  called  the 
vaginal  part,  and  has  a  transverse  oval  aperture, 
called  the  os  uteri,  which  communicates  with  the 
cavity  of  the  uterus.  The  latter  is  a  triangular 


320      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

cavity,  so  flattened  that  the  anterior  and  posterior 
uterine  walls  touch  each  other.  The  base  of  the 
cavity  is  in  the  fundus  and  is  convex  downwards. 
The  two  Fallopian  tubes  open  into  the  upper  angles 
each  by  a  small  aperture  that  will  barely  admit  a 
bristle.  The  cavity  tapers  gradually  toward  the 
cervix,  where  it  becomes  constricted  to  form  the  in- 
ternal os»  The  peritoneum  covers  the  fundus  and 


—  Mucosa. 


Gland. 


—  Muscular  layer 


Serous  layer. 
Fig.  232. — Cross  section  of  wall  of  uterus. 

body  of  the  uterus,  and  posteriorly  extends  down- 
ward to  clothe  the  upper  posterior  wall  of  the  vagina. 
It  is  then  reflected  back  over  the  rectum,  forming  a 
a  sac  called  the  pouch  of  Douglas.  This  makes  it 
possible  to  open  the  peritoneal  cavity  by  a  puncture 
through  the  upper  posterior  vaginal  wall,  an  operation 
which  establishes  free  drainage  to  the  female  pelvis. 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       321 

Anteriorly  the  peritoneum  does  not  cover  the  whole 
uterus,  but  at  the  junction  of  the  body  with  the 
neck,  it  is  reflected  back  over  the  bladder  wall  form- 
ing the  utero-vesical  pouch. 

Structure. — The  histology  of  the  uterus  resembles 
that  of  the  Fallopian  tubes,  and  the  layer  of  the  one 
is  continuous  with  that  of  the  other.  Embryologi- 
cally,  these  two  structures,  and  also  the  vagina,  de- 
velop from  the  Mullerian  ducts,  the  uterus  and 


Muscular  is. 


Fig.  233. — Diagonal  section  of  the  uterine  mucosa. 

vagina  representing  the  fused  lower  ends  of  Muller's 
ducts.  The  whole  uterus,  including  the  epithelial 
lining,  is  therefore  of  mesodermic  origin.  The  uter- 
ine wall  is  composed  of  a  mucosa,  muscular,  and 
serous  layer.  The  Fallopian  tube  has  a  submucosa 
which  is  absent  in  the  uterus. 

The  mucosa,  or  endometrium,  is  the  inner  layer  and 
is  lined  by  simple  columnar  ciliated  epithelium, 
which  at  the  external  os  changes  to  the  stratified 
variety  of  the  vagina.  It  has  a  rich  supply  of 


21 


322      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

branched  tubular  mucous  glands  which,  in  the  cer- 
vix, are  very  large  and  have  a  tendency  to  become 
sacculated.  These  glands  extend  radially  as  far  as 
the  muscularis,  and  some  of  them  may  even  pene- 
trate a  short  distance  into  the  muscle  coat.  The 
gland  ducts  are  lined  by  ciliated  epithelium,  while 
in  the  deeper  portions  cilia  are  absent  and  the  epi- 
thelium becomes  simple  cubical,  resembling  a  glandu- 
lar type.  Most  of  these  glands  take  a  tortuous  or 
spiral  course,  and  are  separated  from  each  other  by 
an  interstitial  tissue  composed  of  connective-tissue 
cells.  These  cells  are  of  the  embryonic  type,  rich  in 
chromatin  and  therefore  stain  heavily  with  nuclear 
dyes.  The  relative  amount  of  interstitial  and 
glandular  tissue  in  a  normal  uterine  mucosa  should 
be  approximately  equal  parts.  The  connective 
tissue  predominates  in  interstitial  endometritis,  and 
the  glandular  tissue  in  adenitis.  The  whole  uterine 
mucosa  is  unusually  thick  and  very  vascular.  In  a 
mature  woman  it  is  normally  subject  to  marked 
periodic  changes  resulting  from  menstrual  condi- 
tions, which  reach  a  high  degree  of  complexity  in 
case  of  pregnancy.  The  action  of  the  cilia  tend  to 
produce  a  downward  movement  of  the  uterine 
secretions  and,  therefore,  opposite  to  the  upward 
movement  of  spermatozoa. 

The  Muscular  Layer. — The  muscularis  is  an  unusu- 
ally thick  layer  of  smooth  muscle  cells  which  in  the 
non-pregnant  uterus  measure  forty  to  sixty  mi- 
crons, while  at  the  end  of  pregnancy  the  cells  measure 
four  hundred  to  six  hundred  microns  in  length. 
These  muscle  cells  are  arranged  in  bundles  with  a 
considerable  amount  of  connective-tissue  fibers  and 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       323 

cells  interlacing  them,  imparting  strength  and  elas- 
ticity to  the  uterine  wall.  There  has  been  consid- 
erable discussion  as  to  the  exact  disposition  of  the 
different  layers  of  this  musculature  which,  in  a  gen- 
eral way,  may  be  divided  into  three  strata:  (i)  an 
inner  layer  of  longitudinal  fibers,  by  some  called 
the  muscularis  mucosa;  (2)  a  middle  circular  layer, 
and  (3)  an  outer  thin  layer  of  fibers  that  run  diago- 
nally or  somewhat  irregularly.  The  inner  layer  is 
much  the  thickest;  none,  however,  is  sharply  de- 
fined. 

The  serous  coat  is  the  peritoneal  lining  which  con- 
sists of  connective- tissue  elements  and  an  invest- 
ment of  simple  pavement  epithelium. 

Vessels  and  Nerves. — The  arteries  that  supply  the 
uterus  are  arranged  in  two  pairs, — the  uterine  and 
ovarian.  The  uterine  artery  is  a  branch  of  the  an- 
terior division  of  the  internal  iliac.  It  reaches  the 
upper  portion  of  the  vagina,  and  then  ascends  in  a 
very  tortuous  manner  along  the  lateral  border  of  the 
uterus  to  the  fundus,  where  it  divides  into  two 
branches,  one  of  which  anastomoses  with  the  ovarian 
artery  and  the  other  supplies  the  Fallopian  tube. 
From  the  ascending  portion  many  side  branches  are 
given  off  which  penetrate  the  uterine  wall  and  ramify 
in  the  muscle  tissue  and  the  mucosa.  These 
branches  are  very  tortuous  so  that  the  uterus 
can  expand  in  pregnancy  without  breaking  the 
vessels. 

The  veins  are  very  large  and  have  no  valves. 
They  form  large  sinuses  mostly  along  the  lateral 
walls,  from  which  the  blood  is  collected  into  two 
trunks:  (i)  the  uterine  vein  accompanies  the  uter- 


324      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

ine  artery  and  empties  into  the  internal  iliac  vein ; 
(2)  vessels  communicate  with  the  ovarian  or  pam- 
piniform  plexus  which  drains  through  the  ovarian 
veins. 

The  lymphatics  begin  in  the  interstitial  substance 
of  the  mucosa,  and  uniting  with  lymphatics  from 
the  muscular  is,  emerge  to  form  a  rich  plexus  just 
beneath  the  serous  covering.  This  plexus  drains 
along  two  channels:  (i)  by  lymphatic  vessels  that 
accompany  the  uterine  veins;  (2)  vessels  that  ac- 
company the  ovarian  veins.  The  blood  and  lymph 
drainage  is  therefore  in  two  directions.  That  of  the 
f undus  is  toward  the  ovary,  and  that  of  the  body  and 
cervix  is  in  the  opposite  direction  along  the  uterine 
vessels.  This  is  of  clinical  importance  in  the  spread 
of  infections. 

The  nerves  are  non-medullated  fibers  from  the  in- 
ferior hypogastric  plexus,  and  medullated  from  the 
third  and  fourth  sacral.  The  non-medullated  sup- 
ply the  muscle  while  the  medullated  fibers  have  been 
traced  to  the  mucosa,  where  they  form  a  plexus  from 
which  fibers  pass  to  the  surface  epithelial  cells.  An- 
other set  arborize  about  the  mucous  gland  cells. 
Sympathetic-nerve  ganglia  are  associated  with  the 
non-medullated  fibers. 

Menstruation. — This  consists  of  a  hemorrhagic  and 
mucous  discharge  from  the  uterus,  which  recurs 
about  every  twenty-eight  days  in  the  non-pregnant 
woman  between  the  ages  of  thirteen  and  forty-five. 
It  is  accompanied  by  more  or  less  severe  systemic 
disturbances  of  a  neurotic  nature,  and  also  by  in- 
creased activity  of  the  glandular  system  as  a  whole, 


REPRODUCTIVE   ORGANS    IN    THE  FEMALE.       325 

Enlargement  of  the  thyroid  gland  usually  accom- 
panies the  menstrual  flow. 

From  five  to  ten  days  before  the  menstrual  flow 
begins  there  is  a  marked  hyperemic  condition  of  the 


C 


Fig.  234. — Uterus  during  menstruation,  cut  open  to  show  the  swelling 
of  the  whole  organ,  and  particularly  the  mucous  membrane:  A,  Mucous 
membrane  of  cervix;  B,  C,  mucous  membrane  of  corpus,  much  thickened; 
D,  muscular  layer;  E,  uterine  opening  of  tube;  F,  os  internum  (the  mu- 
cous membrane  tapers  down  to  these  openings)  (Courty). 

uterine  wall.  The  congestion  of  blood  causes  a 
marked  swelling  and  growth  of  the  uterine  mucosa, 
so  that  it  attains  a  thickness  of  6.0  mm.  This  mu- 
cosa is  then  called  the  decidua  menstrualis.  After 
these  changes  have  occurred  the  menstrual  flow  be- 


326     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

gins  and  usually  lasts  for  four  days.  This  results 
in  a  complete  or  partial  exfoliation  of  the  superficial 
part  of  the  mucous  membrane  of  the  uterine  fundus 
and  body,  but  does  not  involve  the  cervix.  The 
exfoliation  begins  at  the  internal  os  and  advances 
progressively  toward  the  fundus.  The  restoration 
of  the  mucosa  proceeds  in  the  same  order,  from  be- 
low upward,  and  in  the  course  of  five  or  six  days  the 
mucous  membrane  is  restored.  The  epithelial  lining 
regenerates  from  the  free  ends  of  the  mucous  glands 
that  did  not  partake  in  the  exfoliation. 

The  uterus  is  thus  a  seat  of  great  physiological 
activity.  During  at  least  one-half  the  menstrual 
period  of  twenty-eight  days  there  are  marked  struc- 
tural changes  manifest  in  the  uterine  mucosa.  In 
such  an  active  organ  pathological  disturbances  are 
naturally  of  frequent  occurrence. 

Menstruation  and  ovulation  are  related  phenom- 
ena, and  yet  there  is  evidence  that  neither  one  de- 
pends on  the  other.  Pregnancies  may  occur  before 
the  menstrual  period  is  inaugurated.  Even  at  the 
early  age  of  nine  years  pregnancy  has  been  reported ; 
also  in  mature  women  after  confinement,  but  before 
menstruation  has  reappeared,  pregnancy  may  occur. 
A  woman  who  does  not  menstruate  does  not  become 
pregnant,  as  a  rule,  but  there  are  exceptions.  Ovu- 
lation, therefore,  may  go  on  without  menstruation, 
and  there  is  evidence  that  menstruation  may  prevail 
without  ovulation.  For  a  further  discussion  of  this 
subject,  see  Raymond's  "  Human  Physiology." 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       327 

PREGNANCY. 

During  pregnancy  the  mucous  membrane  of  the 
uterus  becomes  modified  into  a  membrane  called  the 
decidua  gramditatis.  This  membrane  may  be  divided 
into  (i)  the  decidua  serotina  or  basalis,  that  part  of 
the  mucosa  to  which  the  ovum  is  attached  and  in 
which  the  placenta  develops;  (2)  the  decidua  re- 
flexa,  that  which  envelops  the  ovum,  and  (3)  the 
decidua  vera,  the  part  that  lines  the  rest  of  the 
uterus. 

In  the  early  stages  of  pregnancy  the  changes  in  the 
uterine  mucosa  resemble  those  of  the  decidua  men- 
strualis.  At  the  end  of  the  first  half  of  pregnancy 
the  decidua  serotina  is  i  cm.  thick.  The  epithelial 
lining  has  disappeared  and  two  layers  can  be  recog- 
nized: (i)  a  superficial  compact  layer,  and  (2)  a  deep 
spongy  layer.  The  compact  layer  consists  of  con- 
nective-tissue elements  and  some  very  large  pig- 
mented  cells  called  the  decidua  cells.  These  cells 
usually  have  one  large  nucleus,  but  some  of  them 
may  be  polynucleated.  The  cells  are  thirty  to  one 
hundred  /*  in  diameter,  and  oval  or  elongated,  re- 
sembling epithelial  cells,  although  they  are  supposed 
to  develop  from  the  interstitial  connective-tissue 
cells  of  the  normal  mucosa.  They  are  of  diagnostic 
value  in  uterine  curetments  where  they  become  a 
probable  evidence  of  pregnancy.  In  post-mortems 
they  have  no  medico-legal  significance,  as  these  cells 
may  be  found  in  the  decidua  menstrualis.  In  the 
spongy  layer  the  connective-tissue  cells  form  septa 
between  the  flattened  and  sacculated  as  well  as  tor- 


328     NORMAI,   HISTOLOGY   AND   ORGANOGRAPHY. 

tuous  mucous  glands.  Blood-vessels  also  form  a 
plexus  in  the  spongy  layer. 

The  decidua  reflexa  disappears  during  the  first 
months  of  pregnancy,  while  the  decidua  serotina 
enters  into  the  formation  of  the  placenta. 

Placenta. — The  placenta  is  a  vascular  organ  for 
the  nourishment  of  the  fetus,  and  serves  the  purpose 
of  bringing  the  fetal  and  maternal  blood  into  closest 
proximity  without  actually  blending.  The  organ 


Villi. 


.:-•  '  ••^'  ~'2J^4-  *"«*•';-*-* ^*  ^>  ^s^         Compact  layer  of  de- 
-*  +  ffx*£r£-  "^r^ '  .~~  -Vt  T'.         cidua  with  decidual 

i~-  ~  ^  .*~  ^~   ^r7^-  "*  '."'^•^L^-- ' 


Spongy  layer  of  de- 
cidua -with  gland 
spaces. 


Fig.  235. — Section  of  the  decidua  serotina  at  the  margin  of  the  placenta. 

may  be  divided  into  an  embryonic  part,  the  placenta 
jcetalis,  and  a  maternal  part,  the  placenta  materna. 
The  latter  is  the  modified  uterine  mucosa  or  decidua 
serotina. 

The  fertilized  ovum  usually  finds  lodgment  in  the 
fundus  of  the  uterus.  Very  early  it  becomes  en- 
closed in  an  envelope  of  its  own  production  called 
the  chorion.  This  chorion  has  an  outer  epithelial 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       329 


Blood  capillaries. 


Zellknoten. 


layer  and  an  inner  connective-tissue  layer,  the  latter 
being  vascular.  It  is  this  vascular  chorion  that  enters 
into  intimate  relations  with  the  uterine  mucosa 
to  form  the  placenta,  the  former  the  fetal  part  and 
the  latter  the  maternal  part.  These  parts  become 
intimately  associated. 

The  chorion  very  early  produces  a  large  number  of 
villi  which  invade  the  mucosa,  where  they  ultimately 
become  large  and  much  branched,  like  the  root  of  a 
tree.  These  are  the  chorionic  villi  and  belong  to 
the  fetal  pla- 
centa. Each 
villus  consists 
of  a  connective- 
tissue  core  with 
an  epithelial 
lining.  The 
fetal  blood  cir- 
culates through 
the  connective- 
tissue  core 
while  the  maternal  blood  bathes  the  external  sur- 
faces of  the  villi.  The  terminal  ramifications  of 
each  villus  becomes  firmly  anchored  iii  the  uterine 
mucosa,  while  the  branched  lateral  twigs  float  freely 
in  the  maternal  blood  spaces  or  intervillus  sinuses. 
These  villi  serve  a  double  purpose.  They  attach 
the  fetal  placenta  firmly  to  the  uterus,  and  establish 
a  close  relation  between  fetal  and  maternal  blood 
whereby  the  embryo  receives  proper  nourishment. 
Upon  closer  examination  each  villus  should  present 
in  cross  section  an  outer  layer  of  simple  squamous 


Syncytium  or 
protoplasmic 
coat. 


Epithelial  cells. 

Fig.  236. — Cross  section  of  two  human  chorionic 
villi  at  end  of  pregnancy. 


330      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

epithelial  cells  and  a  core  of  connective-tissue  cells 
in  which  two  or  more  small  capillary  blood-vessels 
ramify.  The  epithelium  of  the  villi  undergoes  great 
alterations  and  may  entirely  disappear,  to  be  re- 
placed by  isolated  accumulations  of  large  round 
nuclei  that  stain  intensely  with  nuclear  dyes,  and 
that  form  protuberances  on  the  surfaces  particularly 
of  the  large  villi.  These  are  called  zellknoten,  or 
cell  knots.  Their  origin  and  significance  is  doubtful. 
In  the  earlier  months  of  pregnancy  the  epithelial  in- 
vestment of  each  villus  is  clothed  externally  by  a 
continuous  protoplasmic  mass,  called  the  syncytium, 
containing  small  and  irregularly  scattered  nuclei. 
It  is  generally  supposed  that  the  syncytium  repre- 
sents the  modified  and  disintegrated  uterine  epi- 
thelium and  is  therefore  of  maternal  origin.  Some 
embryologists  affirm  that  in  some  villi  there  is  a 
membrane  external  to  the  syncytium  which  mor- 
phologically represents  the  epithelial  wall  of  the 
uterine  blood-vessels.  The  maternal  blood,  how- 
ever, very  soon  breaks  through  the  capillary  spaces 
of  the  uterine  mucosa  and  enters  the  intervillus 
sinuses  clothed  by  the  syncytium.  The  fetal  cir- 
culation is  a  closed  system  and  nowhere  is  there  a 
direct  intermingling  of  fetal  and  maternal  blood.  The- 
oretically the  exchange  of  gases,  in  the  early  stages 
of  development,  takes  place  through  (i)  the  epi- 
thelial wall  of  the  maternal  capillaries;  (2)  the  uter- 
ine epithelial  lining,  probably  represented  by  the 
syncytium;  (3)  the  epithelial  lining  of  the  chorion, 
and  (4)  the  epithelial  wall  of  the  fetal  blood  capilla- 
ries. The  first  of  these  membranes  is  not  always 


PLATE  VI. 


B2*1 

O    p    "^cra     M 

ct-£3     O 
>P    O    «    g     ^ 


(D     &:<"*-.     hrj 

^  a- «.  ff  a 

rj    3    CD  HH 


tr*  p   a*  <->-    O 
«   o    p   <5     ^ 

3|~i.a 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       331 

present,  as  maternal  blood  ruptures  this  wall.  The 
second  investment,  or  syncytium,  disintegrates. 
The  third  also  disappears,  at  least  in  parts,  or  be- 
comes so  thin  that  it  can  scarcely  be  detected.  Ulti- 
mately, therefore,  the  fetal  and  maternal  blood  is 
practically  separated  by  only  one  membrane,  the 
epithelium  of  the  fetal  capillaries. 

The  maternal  placenta  does  not  differ  structurally 
from  the  histology  of  the  decidua  already  described 
except  in  degree  of  complexity.  There  is  an  inter- 
nal compact  portion  and  a  deeper  spongy  layer.  The 
latter  rests  against  the  uterine  muscularis  and  is  very 
vascular.  Numerous  blood- 
vessels penetrate  the  compact 
layer  to  open  freely  into  the 
intervillus  sinuses  already  de- 
scribed. These  blood-vessels 
usually  take  a  very  tortuous 
course,  and  they  are  thus  able 

to  adjust  themselves  to  contractions  and  expansions 
of  the  uterine  wall.  Decidual  cells  are  especially 
conspicuous  in  the  compact  layer  of  the  placenta. 
These  cells  are  sometimes  present  in  the  spongy 
layer  but  never  in  the  chorionic  villi  or  fetal  portions 
of  the  placenta. 

The  fetal  blood  reaches  the  placenta  through  the 
umbilical  cord.  There  is  regularly  present  two  ar- 
teries and  one  vein,  imbedded  in  a  gelatinous  con- 
nective-tissue matrix  known  as  Wharton's  jelly. 
The  blood  in  the  arteries  is  carried  to  the  placenta 
and  is  venous.  That  in  the  vein  returns  from  the 
placenta  and  is  arterial.  After  birth,  when  the  pla- 


33 2      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

centa  comes  away,  it  is  always  at. the  expense  of  the 
uterine  mucosa,  which  leaves  a  raw,  bleeding  surface. 
The  uterine  muscles  at  once  contract,  reducing  the 
uterine  cavity  and  checking  the  hemorrhage.  A 
normal  mucous  membrane  at  once  regenerates,  the 
ciliated  epithelium  and  mucous  glands  developing 
from  remnants  of  glands  that  were  not  entirely  ob- 
literated by  the  placental  growth.  As  a  rule  regular 
menstruation  is  inaugurated  when  lactation  ceases, 
but  there  are  exceptions  to  this.  A  second  preg- 
nancy may  follow  without  any  intervening  menstrual 
period,  but  this  is  rare. 

THE  MAMMARY  GLAND* 

The  mammary  gland  is  a  skin  gland  that  is  present 
in  both  sexes.  In  the  second  month  of  embryonic 
life  there  is  a  linear  thickening  of  the  skin,  extending 
from  each  axilla  to  the  groin,  and  at  regular  inter- 
vals in  this  ridge  a  series  of  mammary  glands  develop 
in  many  vertebrates.  In  the  human  race  only  one 
pair  is  produced,  which  represents  the  fourth  or  fifth 
pair  of  this  series.  In  rare  cases  accessory  mam- 
mary glands  are  found  in  man  both  above  and  below 
the  normal  pair. 

In  childhood  the  mammary  gland  is  identical  in 
both  sexes,  but  with  approaching  puberty  it  enlarges 
in  the  female,  reaching  its  highest  development  at 
the  end  of  pregnancy.  The  menopause  brings 
about  a  retrogression  and  shrinkage  of  the  organ. 
The  gland  is  therefore  to  be  considered  an  accessory 
sexual  organ. 

The  mammary  gland  is  a  segregation  of  fifteen  to 


REPRODUCTIVE   ORGANS   IN   THE   FEMALE.       333 


twenty  separate  compound  tubulo-alveolar '  glands 
which  open  separately  on  the  nipple  by  an  equal 
number  of  pores.  These  glands  are  arranged  radi- 
ally and  enclosed  by  a  variable  supply  of  fat  and 
connective  tissue  in  such  a  way  that  it  is  possible  to 
divide  the  breast  into  fifteen  to  twenty  lobes,  which 
may  be  further  divided  into  lobules.  Each  pore 
leads  to  a  narrow 
vertical  tube,  the 
lactiferous  duct, 
which  widens  just 
below  the  base  of 
the  nipple  to  form 
a  receptacle  called 
the  milk  sinus,  be- 
yond which  it 
again  becomes  a 
narrow  tube. 
The  latter  be- 
comes branched  to 
form  interlobular 
ducts  that  open 
into  distal  dilata- 
tions or  alveoli,  which  constitute  the  secreting  por- 
tions of  the  gland. 

The  lactiferous  ducts  and  sinus  are  lined  with 
simple  columnar  epithelium,  which  becomes  strati- 
fied near  the  orifices  where  it  is  directly  continuous 
with  the  stratified  epithelium  of  the  skin.  The  finer 
structure  of  the  alveoli  varies  according  to  the  func- 
tional activity  of  the  organ.  During  lactation  the 
alveoli  are  distended  with  milk.  The  cells  of  the 


Lactiferous  duct. 
•Milk  sinus. 


Alveoli. 


Fig.  238. — Diagram  of  one-half  of  mammary 
gland,  dissected  to  show  gland. 


334     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

simple  glandular  epithelium  become  distended  with 
the  products  of  secretion  that  consist  of  granules  and 
deposits  of  fat.  The  granules  liquefy  and  along  with 
the  fat  globules  are  discharged  into  the  alveoli  as 
milk.  Many  particles  of  fat  are  taken  up  by  migra- 
ting white  corpuscles,  called  phagocytes,  which  mix 
with  the  secretion  and  thus  become  converted  into 
the  colostrum  corpuscles  of  early  lactation.  The 
gland  cells  after  secretion  accumulate  a  second  sup- 


;  cells. 


Connective  tissue 


Gland  alveoli. 


Fig.  239. — Section  of  a  portion  of  the  mammary  gland. 

ply,  and  this  process  is  repeated  many  times.  The 
secreting  cell  does  not  disintegrate  as  is  the  case  in 
the  sebaceous  glands  of  the  skin. 

When  the  gland  is  not  engaged  in  the  secretion  of 
milk,  many  of  the  alveoli  shrink  up  and  disappear, 
while  the  remaining  ones  become  much  reduced  in 
size,  and  the  gland  as  a  whole  is  smaller.  The  cells 
of  the  alveoli  become  columnar,  resembling  the  cells 
that  line  the  ducts.  The  epithelium  rests  upon  a 


REPRODUCTIVE   ORGANS  IN  THE   FEMALE.       335 

basement  membrane  and  a  membrana  propria,  the 
latter  containing  basket  cells  whose  processes  mingle 
with  the  glandular  epithelium. 

The  interstitial  tissue  just  external  to  the  alveoli 
is  composed  of  connective-tissue  cells  that  stain 
heavily  with  nuclear  dyes,  while  in  the  intervening 
spaces  between  the  alveoli,  connective-tissue  fibers 
and  fat  cells  are  abundant.  A  supply  of  plain  muscle 
fibers  intervene  and  surround  the  ducts  in  the  nip- 
ple. The  fibers  placed  longitudinally  function  in 
the  erection  of  the  nipple,  while  the  circular  ones 
constrict  the  ducts. 

The    nipple  does    not  Epithelial  Connective-tissue 

1           1  .  .  1  r  .  cells.  cells. 

develop  until  after 
birth.  Its  normal  po- 
sition is  in  the  fourth  in- 
tercostal space,  about 
four  inches  from  the 
sternum.  It  is  clothed 

with     Stratified     pig-      Fig.  240.— Section  through  two  alveoli 

mented  epithelium  and 
devoid  of  hair  follicles 

and  sweat  glands.  The  skin  immediately  around 
the  nipple  is  also  pigmented,  forming  an  areola  with 
numerous  small  papillae,  giving  a  rough  or  wrinkled 
appearance.  Besides  large  sweat  glands,  twelve  or 
more  large  sebaceous  glands,  called  glands  of  Mont- 
gomery, are  present  in  this  area.  These  glands  open 
at  the  apices  of  the  small  papillae  just  mentioned, 
and  are  usually  considered  as  accessory  milk  glands. 
Vessels  and  Nerves. — The  arteries  that  supply  tl^ 
breasts  are  the  long  thoracic,  the  internal  mammary, 


336     NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

and  the  intercostals.  These  anastomose  freely  and 
approach  the  gland  from  all  directions.  The  veins 
are  equally  extensive.  They  accompany  the  arteries 
and  bear  the  same  names.  Lymphatics  are  very 
numerous  and  form  extensive  lymph  spaces  around 
the  alveoli  of  the  gland.  For  the  most  part  they 
drain  to  the  lymph  glands  in  the  axilla,  but  from  the 
deeper  part  of  the  breast  they  drain  along  the  course 
of  the  internal  mammary  artery. 


CHAPTER  X. 
THE  SKIN. 

The  skin  covers  the  entire  body  and  is  directly 
continuous  with  the  mucous  membranes  of  the  ali- 
mentary canal  and  urogenital  organs  at  their 
external  orifices.  It  contains  sensory  nerve  endings 
and  in  the  deeper  layers  there  is  a  liberal  supply  of 
both  blood-  and  lymph- vessels.  It  is  the  chief  factor 
in  regulating  body  temperature,  and  is  an  efficient 
mechanical  protection  to  the  deeper  tissues,  while  the 
sweat  and  sebaceous  glands  render  it  an  important 
excretory  organ.  Hairs  and  nails  represent  modi- 
fications of  the  superficial  layers.  It  varies  consid- 
erably in  thickness,  being  4  mm.  thick  on  the  palms 
of  the  hand  and  0.5  mm.  over  the  back  and  shoul- 
ders. The  color  is  imparted  by  pigmentation  and 
the  blood  supply.  The  color  is  characteristic  of  races 
and  variable  in  the  different  parts  of  the  body  as  well 
as  subject  to  modification  depending  on  age  and  dis- 
ease. The  skin  moves  freely  upon  the  deeper  tissues, 
excepting  over  bony  prominences  where  it  is  more 
firmly  attached.  On  the  palm  of  the  hand  and  the 
sole  of  the  foot  it  is  also  bound  down  to  the  subjacent 
tissues.  The  external  surface  presents  in  places 
numerous  permanent  ridges  which  correspond  with 
rows  of  underlying  papillae,  and  which  in  criminals 
are  utilized  for  the  purposes  of  identification.  The 

22  337 


338      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

hair  follicles  appear  with  regularity  in  external  de- 
pressions practically  all  over  the  body,  forming  dis- 
tinctive patterns.  Cutaneous  blood-vessels  and 


Sweat  gland. 


Corneum. 


Stratum  lucidum. 
Stratum  granulosum. 


?   Malpighian  layer. 


Papilla  of  dermis. 


Dermis. 


Fat  cells. 

>  Sweat  gland. 
Fig.  241. — Section  of  skin  through  palmar  surface  of  fingers. 

tendons  form  ridges  and  lines  readily  detected  by 
the  unaided  £ye,  and  over  which  the  skin  is  freely 
movable. 


THE    SKIN.  339 

Structurally  the  skin  or  integument  consists  of 
two  chief  strata  that  may  be  subdivided  into  layers 
in  the  following  manner: 

I.  Epidermis  epithelial    layers  derived  from  the 
ectoderm. 

1.  Corneum    or    horny    layer, — superficial 

epithelial  plates. 

2.  Stratum   lucidum, — absent    where   the 

skin  is  thin. 

3.  Stratum  granulosum, — absent  where  the 

skin  is  thin. 

4.  Malpighian   or   germinal   layer, — nucle- 

ated growing  cells. 

II.  Dermis  or  corium, — connective-tissue  elements 
from  the  mesoderm. 

1.  Papillary  layer. 

2.  Reticular  layer. 

Epidermis. — The  horny  layer  of  the  epidermis 
forms  the  outer  covering  of  the  skin  and  consists  of 
several  layers  of  scaly  epithelial  cells  in  which  the 
nuclei  have  disappeared.  The  cells  are  dead  and 
constantly  exfoliating  superficially,  while  new  strata 
are  regularly  added  from  below.  Bacteria  are 
usually  present  in  its  external  parts,  and  in  surgi- 
cal operations,  therefore,  the  skin  is  thoroughly 
scrubbed,  a  process  that  removes  most  of  this  layer 
and  renders  the  field  of  operation  practically  sterile. 
At  birth  the  horny  layer  is  less  compact  and  of  a  red 
color.  It  is  then  called  the  vernix  caseosa,  which 
exfoliates  in  a  few  days,  when  the  complexion 


340      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

changes  to  that  of  the  particular  race  to  which  the 
child  belongs. 

The  strata  lucidum  and  granulosum  are  two  thin 
layers  that  lie  between  the  cortieum  and  the  Mal- 
pighian  layers  and  are  best  developed  in  the  sole  of 
the  foot  and  the  palm  of  the  hand.  Each  consists 
of  two  or  three  rows  of  epithelial  cells.  The  stratum 
lucidum  overlies  the  stratum  granulosum  and  is  a 
refractive  layer  consisting  of  cells  with  disintegrating 


J-^ ^j=i_ — - 1__^~.  t!~r=r='-^2^,' Corncum  or  horny  layer. 


Stratum  lucidum. 
Stratum  granulosum. 


Malpi^hian  or  germinal 
layer. 


Fig.  242. — Section  of  epidermis  of  skin  from  palm  surface  of  finger. 

nuclei,  and  possessing  a  homogeneous  substance 
called  eleidin.  The  latter  is  colored  with  eosin  but 
does  not  take  nuclear  dyes.  The  cells  that  compose 
the  stratum  granulosum  possess  many  granules 
called  keratohyalin  granules,  which  are  regarded  as 
products  of  cell  disintegration.  These  granules  in- 
crease in  size  and  coalesce  to  form  the  semifluid  sub- 
stance called  eleidin  of  the  stratum  lucidum.  The 
granules  take  nuclear  dyes;  the  eleidin  does  not. 


THE   SKIN.  341 

The  Malpighian  layer  is  made  up  of  growing  epi- 
thelial cells  and  constitutes  the  deeper  parts  of  the 
epidermis.  Its  lower  surface  is  beset  with  numerous 
depressions  that  receive  connective-tissue  papillae 
from  the  dermis.  The  epidermis  and  dermis  thus 
interlock  by  means  of  an  extensive  system  of  papillae 
from  each  layer.  The  Malpighian  layer  is  thicker  than 
the  horny  layer,  excepting  in  the  sole  of  the  foot  and 
the  palm  of  the  hand.  It  consists  of  ten  to  fifteen 
layers  of  epithelial  cells.  The  cells  in  the  lower  row 
are  columnar  and  are  so  arranged  that  their  long  axis 
is  vertical  to  that  surface.  In  colored  races  these 
cells  are  pigmented  and  impart  to  the  skin  the  par- 
ticular color  of  the  race.  Pigmentation  has  been 
discussed  on  page  73,  to  which  the  reader  is  re- 
ferred. The  other  cells  of  the  Malpighian  layer  are 
cubical  or  flattened  and  so  placed  that  their  long 
axis  lies  parallel  to  the  surface  of  the  body.  The 
cells  of  the  deeper  strata  have  numerous  minute 
short  processes  and  have  been  called  prickle  cells. 
These  processes  form  intercellular  bridges,  which 
give  rise  to  a  complex  system  of  minute  intercellular 
channels  that  permit  more  freely  the  passage  of 
nourishment.  These  cells  are  constantly  dividing 
and  adding  new  strata  to  the  horny  layer  that  is  ex- 
foliating at  the  same  rate. 

The  dermis,  corium,  or  cutis  vera,  is  of  connective- 
tissue  origin  and  lies  just  beneath  and  intimately 
associated  with  the  epidermis.  It  may  be  divided 
into  a  papillary  portion,  next  to  the  epidermis,  and 
a  deeper  reticular  portion  which  shades  off  into  the 
subdermal  fascia.  The  papillary  portion  consists  of 


342     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

vascular  and  nerve  papillae  that  fit  into  depressions 
on  the  lower  surface  of  the  epidermis.  The  two 
layers  of  the  dermis  pass  into  each  other  without  any 
sharp  line  of  demarcation.  In  both  layers  there  is 
an  abundance  of  connective-tissue  fibers,  both  elastic 
and  non-elastic,  forming  what  has  been  termed  areo- 
lar  tissue.  These  fibers  form  bundles  that  interlace 
to  produce  a  network,  particularly  in  the  reticular 
or  deep  portions.  In  the  meshes  of  this  reticulum 
are  to  be  found  the  bodies  of  the  sweat  glands,  and  a 
variable  amount  of  adipose  tissue,  while  hair  follicles 
with  their  sebaceous  glands  find  lodgment  in  the 
dermis  with  greater  regularity.  It  is  the  dermis , 
and  particularly  the  areolar  tissue,  that  gives  elas- 
ticity and  mobility  to  the  skin.  The  epidermis  is 
not  very  elastic,  consequently  wrinkles  of  the  epi- 
dermis are  formed  when  the  fat  is  absorbed,  and 
also  in  old  age,  by  shrinkage  of  the  areolar  tissue. 

A  variable  amount  of  muscle  is  everywhere  present 
in  the  dermis.  Smooth  muscle  is  associated  with 
the  hair  follicles,  forming  the  arrector  pili  muscle. 
In  the  face  and  neck  voluntary  muscle  fibers  may  be 
traced  into  the  papillary  layer,  while  a  third  set  of 
muscle  elements  is  associated  with  the  sweat  glands. 
The  latter  is  of  the  smooth  variety  and  will  be  de- 
scribed along  with  the  sweat  glands. 

The  dermis  everywhere  is  very  vascular.  Blood- 
and  lymph- vessels  ramify  freely  through  it,  but  in 
no  case  do  they  enter  the  epidermis.  Nerve  fibers, 
on  the  other  hand,  enter  the  Malpighian  layer  of  the 
epidermis  and  arborize  around  and  between  the 
epithelial  cells.  In  the  dermis  these  fibers  form  an 


THE   SKIN. 


343 


Medulla. 


extensive  nerve  plexus,  from  which  some  terminal 
fibers  proceed  to  the  hair  follicles,  and  others  to 
special  nerve  papillae  in  the  dermis.  These  and 
other  nerve  terminations  will  be  described  as 
peripheral  nerve  endings  in  another  chapter. 

HAIRS. 

The  hairs  are  distributed  practically  over  the 
whole  surface  of  the  body,  with  the  exception  of  the 
palms  of  the  hand,  the  soles  of  the  feet,  and  the  red 
border  of  the  lips.  They  are  distributed  with  con- 
siderable regularity,  as  a 
rule  one  hair  for  each  fol- 
licle, but  there  may  be  two 
and  sometimes  three.  The 
part  of  the  hair  buried  in 
the  skin  is  called  the  root, 
and  the  part  that  projects 
beyond  the  surface  is  the 
shaft.  The  lower  part  of  the 
root  is  thickened  to  form 
the  hair  bulb,  into  which  is 
pushed  from  below  a  vascu- 
lar connective-tissue  projection  called  the  hair  papil- 
la. The  root  is  inserted  deep  in  the  skin,  usually 
reaching  the  subdermal  elements.  It  is  placed 
diagonally  to  the  surface  and  becomes  enclosed  in  a 
specially  modified  wall  made  up  of  several  layers  de- 
rived partly  from  the  epidermis  and  partly  from  the 
dermis. 

Most  hairs  are  composed  of  three  layers :  an  outer 
cuticle,  a  middle  cortical,  and  a  central  portion,  the 


Cortical  layer. 


Hair  cuticle. 


Fig.   243. — Portion  of  a  hair. 


344     NORMAL,   HISTOLOGY   AND   ORGAN  OGRAPHY. 

medulla.  In  thin  and  light  hairs  the  medulla  is  usu- 
ally absent. 

The  hair  cuticle,  or  outer  hair  membrane,  is  made  up 
of  structureless  transparent  epithelial  scales  that 
overlap  each  other  in  the  direction  of  the  distal  end 
of  the  hair.  A  hair  feels  smooth,  therefore,  if  pulled 
through  the  fingers  from  the  root  to  the  free  end. 
These  scales  overlap  each  other  sometimes  to  such 
an  extent  that  the  cuticle  has  the  appearance  of 
being  stratified.  The  scales  are  derived  from  epi- 
thelial cells  that  have  become  cornified,  and  they 
are  thus  closely  related  to  the  horny  epithelial  plates 
of  the  epidermis. 

The  cortical  substance  forms  the  main  bulk  of  the 
hair  and  lies  just  beneath  the  cuticle.  The  cortex 
consists  of  spindle-shaped  nucleated  cells  which 
show  a  distinct  fibrillar  structure,  giving  the  whole 
hair  the  appearance  of  being  longitudinally  striated. 
Pigment  granules  are  deposited  in  these  cells  and 
between  them,  to  which  the  hair  owes  most  of  its 
color.  Numerous  small  spaces  filled  with  air  are 
frequently  formed  between  the  cells  of  the  cortical 
layer,  and  these  give  a  white  color  to  hairs  that  have 
a  scanty  supply  of  pigment.  Hairs  that  have  en- 
tirely lost  their  pigment  and  have  none  of  these  air 
spaces,  are  gray  but  not  white. 

The  medullary  substance  forms  the  axis  of  the 
hair  and  may  be  absent,  but  is  usually  present  in 
thick  hairs.  It  is  made  up  of  nucleated  cubical 
epithelial  cells  forming  two  or  three  rows  in  thick- 
ness. Pigment  is  also  present  in  the  medullary 
cells. 


THE   SKIN. 


345 


Hair  Follicles. — The  hair  follicles  are  the  pits  in  the 
skin  occupied  by  the  roots  of  the  hairs.  These  pits 
are  placed  diagonally  to  the  surface,  and  in  the  scalp 
where  the  skin  is  thick  they  are  at  least  half  an  inch 
in  length.  It  is  estimated  that  the  normal  scalp 
has  about  one  hundred  and  twenty  thousand  of  these 
follicles,  or  an  average  of  eight  hundred  to  the  square 
inch.  Each  follicle  is  really  a  minute  tubular  de- 


Longitudinal  connective-tissue  fibers. 
Circular  fibers. 
Glassy  membrane. 

Outer  root  sheath. 

Henle's  layer. 
Huxley's  layer. 
Inner  root  sheath. 


Hair  shaft. 


Fig.  244. — Cross  section  of  a  hair  follicle. 

pression  or  invagination  of  the  skin,  and  its  wall  is 
therefore  made  up  of  constituents  from  both  the  epi- 
dermis and  the  dermis.  These  layers  may  be  tabu- 
lated as  follows : 

I.  Outer  tunic. 

1.  Connective-tissue  fibers  arranged  longi- 

tudinally. 

2.  Connective-tissue  fibers,  circular. 

3.  Glassy  membrane. 


346     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

II.  Outer    root    sheath;     resembles    Malpighian 
layer  of  the  epidermis. 
III.  Inner  root  sheath. 

1.  Henle's     layer, —non-nucleated     ele- 

ments. 

2.  Huxley's  layer, — nucleated  cells. 

3.  Root  sheath, — structureless  membrane. 
The  outer  tunic  is  derived  from  the  dermis  and  is 

of  connective-tissue  origin.  Externally  there  is  a 
layer  of  connective-tissue  fibers  arranged  longitudi- 
nally, in  which  may  be  found  a  few  connective- 
tissue  cells  and  a  delicate  plexus  of  nerve  fibers. 
The  non-elastic  connective-tissue  fibers  predominate, 
but  the  elastic  variety  is  also  present.  Internal  to 
the  longitudinal  fibers  is  a  compact  circular  layer  of 
non-elastic  connective-tissue  fibers,  and  internal  to 
this  is  the  glassy  membrane,  a  very  thin  hyaline 
sheath  often  difficult  to  find.  The  outer  tunic  in- 
vests the  lower  half  of-  the  root  sheath.  This  tunic, 
in  the  so-called  tactile  hairs  of  many  mammals,  has  a 
rich  nerve  innervation  and  a  liberal  blood  supply. 
In  such  hairs  nerve  fibers  have  been  traced  to  the 
glassy  membrane,  while  others  apparently  penetrate 
to  tactile  cells  in  the  outer  root  sheath. 

The  root  sheaths  encase  the  root  of  the  hairs  and 
are  derived  from  the  epidermis,  being  therefore  of 
ectodermal  origin.  The  outer  root  sheath  is  a  direct 
continuation  of  the  Malpighian  layer  and  diminishes 
in  thickness  toward  the  bottom  of  the  follicle.  It  is 
composed  of  nucleated  epithelial  cells  which  possess 
intercellular  bridges  and  a  fibrillar  protoplasm. 
This  sheath  always  stains  heavily  with  nuclear  dyes, 


THE   SKIN. 


347 


The  inner  root  sheath  is  less  conspicuous,  and  in  good 
sections  will  be  found  to  consist  of  an  outer  layer  of 
two  rows  of  non-nucleated  elements,  representing 
cornified  epithelial  cells  and  called  Henle's  layer,  and 


Hair  shaft. 


Epidermis. 


Sebaceous  gland. 


Fat  cells.  Hair  papilla. 

Fig.  245. — Cross  section  of  the  human  scalp. 

internal  to  this  about  two  rows  of  nucleated  cells, 
called  Huxley's  layer.  These  layers  are  absent  from 
the  upper  half  of  the  follicle.  Internal  to  Huxley's 
layer,  and  in  direct  contact  with  the  root  of  the  hair, 
is  the  root  sheath,  which  has  much  the  same  structure 
as  the  hair  cuticle.  Many  scaly  plates  are  imbricated 


348        NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

upon  each  other  and  interlock  with  those  of  the  hait 
cuticle  in  such  a  manner  that  if  a  hair  is  pulled  out 
the  root  sheath  comes  away  with  it,  the  break  taking 
place  along  Huxley's  and  Henle's  layers. 

The  hair  papilla  indents  the  lower  end  of  the  root 
and  is  of  connective-tissue  origin.  It  has  a  rich 
blood  supply  which  contributes  nourishment  to  the 
adjacent  epithelial  cells  of  the  root  which  are  con- 
stantly dividing.  It  is  this  cell  division  that  brings 
about  the  growth  of  a  hair.  If  the  papilla  is  de- 
stroyed the  hair  dies.  When  a  hair  is  pulled  out 
with  its  root  the  papilla  and  some  adjacent  epithelial 
cells  usually  remain  uninjured.  The  epithelial  cells 
in  due  time  reproduce  a  new  hair. 

The  arrector  pili  muscle  consists  of  bundles  of 
smooth  muscle  fibers  that  pass  obliquely  downward 
from  the  upper  surface  of  the  dermis  to  be  inserted 
in  the  connective-tissue  tunic  of  the  hair  follicle  near 
its  lower  extremity.  The  insertion  of  these  fibers  is 
always  on  the  side  toward  which  the  hair  inclines,  so 
that  when  the  fibers  contract  the  root  is  drawn  to  a 
vertical  position  and  the  hair  becomes  erect. 

The  hair  on  the  scalp  grows  approximately  at  the 
rate  of  twelve  inches  a  year,  or  one  inch  a  month. 
The  average  duration  of  a  hair  is  about  four  years. 
Many  vertebrates,  as  horses  and  cattle,  shed  their 
hair  annually,  every  spring,  a  phenomenon  called 
moulting.  In  mankind  the  hair  of  the  scalp  is  con- 
stantly dropping  out  and  being  replaced  by  growths 
of  new  shafts.  Occasionally  hair  grows  where  it 
normally  does  not  belong  and  for  cosmetic  effect 
requires  removal.  This  is  done  by  electrolysis, 


THE  SKIN.  349 

which  consists  in  passing  an  electric  needle  down 
along  the  root  of  each  hair  to  the  hair  papilla,  which 
is  then  destroyed  by  a  weak  current  of  electricity. 
The  hair  is  then  readily  removed  and  does  not  re- 
turn. The  loss  of  hair  on  the  scalp  is  due  to  a  va- 
riety of  causes,  many  of  which  we  cannot  explain. 
It  often  accompanies  a  prolonged  illness,  such  as 
typhoid  fever,  and  is  then  doubtless  due  to  a  general 
emaciation  resulting  in  lack  of  proper  nourishment 
of  the  scalp.  The  loss  of  hair  in  such  cases  is  only 
temporary.  Certain  neurotic  diseases  result  in  a 
permanent  loss  and  the  same  may  be  attributed  to 
some  germ  diseases  of  the  scalp  that  infest  and  de- 
stroy the  hair  papillae.  In  other  cases  baldness 
seems  to  be  hereditary.  It  naturally  follows  that  a 
healthy  condition  of  the  scalp  will  contribute  to  a 
rich  growth  of  hair.  Regular  massage  with  a  stiff 
brush  no  doubt  accelerates  the  blood  flow  and  thus 
brings  about  a  better  nourishment  and  growth  to  the 
hair. 

The  natural  preservation  of  hair  after  death  is 
well  known.  In  Egyptian  mummies  the  hair  is  well 
preserved  even  to  its  natural  color.  The  hair  is  thus 
an  important  factor  in  the  identification  of  unknown 
deceased  persons. 

THE  NAILS. 

The  nails  are  epidermal  structures  that  are  mor- 
phologically analogous  to  the  hoofs  and  claws  of 
lower  animals.  Each  nail  may  be  divided  into  a 
body,  the  part  that  is  exposed,  and  the  root  that  is 
hidden  from  view  and  lies  in  a  fold  of  the  skin.  The 


350     NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 


lateral  margins  are  also  covered  by  a  fold  of  the  skin 
called  the  nail  wall.  The  nails  have  a  pink  color 
imparted  by  the  subjacent  blood,  excepting  near  the 
root,  where  there  is  an  opaque  area  called  the  lunula. 
The  lunulae  diminish  in  size  from  the  thumb  to  the 
little  finger. 

Each  nail  rests  upon  a  very  vascular  dermis  which 
has  been  called  the  nail  bed 
or  matrix.  This  connective- 
tissue  bed  has  many  fine 
longitudinal  ridges  and 
alternating  grooves  which 
fit  closely  into  correspond- 
ing grooves  and  ridges  on 
the  lower  surface  of  the 

nail.  Each  nail  consists  of  two  parts:  a  deep  soft 
stratum  that  represents  the  Malpighian  layer  of  the 
epidermis,  and  an  external  hard  cornified  layer  that 


Body  of  nail. 


Fig.  246. — Thumb  nail. 


Body  of  nail. 


Root  of  nail. 


Mantle. 


Phalanx. 


Nail  bed. 
Fig.  247. — Longitudinal  section  of  nail. 

represents  the  horny  layer.  The  former  consists  of 
nucleated  polygonal  prickle  cells  which  fill  the  fur- 
rows and  cover  the  nail  bed  several  cells  deep.  It  is 
affirmed  that  the  cells  of  this  Malpighian  layer,  in 
the  distal  part  of  the  nail,  do  not  produce  any  of  the 
overlying  horny  material,  but  that  growth  of  the  nail 


THE   SKIN. 


351 


Nail  wall. 


Fig.  248. — Cross  section  of  nail. 


is  exclusively  due  to  epithelial  proliferation  from  the 
Malpighian  layer  at  the  root  of  the  nail  and  from 
that  part  directly  under  each  lunula  already  de- 
scribed. A  stratum  granulosum  is  present  in  the 
upper  portion  of  the  matrix  and  absent  in  the 
other  portions  of  the  nail. 

The  external  cor- 
nified  layer  consists 
of  flat  epithelial 
scales  in  which  rem- 
nants of  a  nucleus 
may  frequently  be 
found.  These  scales 
are  derived  from 
epithelial  cells  and 

overlie  each  other,  forming  hardened  lamellae  called 
nail  leaves. 

The  hoof  of  the  horse  corresponds  to  the  finger- 
nail of  man,  and  is  divided  for  descriptive  purposes 
into  the  wall,  the  sole  and  the  frog.  The  part  which 
is  visible  when  the  foot  rests  on  the  ground  is  the 
wall,  while  the  sole  and  frog  are  invisible  in  this 
position.  As  the  human  nail  rests  on  a  grooved 
matrix,  so  the  inner  surface  of  hoof  wall  is  extensively 
folded  into  leaf-like  structures  which  interlock  or 
digitate  with  like  growths  from  the  enclosed  con- 
nective tissue,  those  from  the  wall  being  called  horny 
or  insensitive  lamina,  and  those  from  the  connective 
tissue  or  dermis  the  sensitive  or  vascular  lamina. 

Horny  Lamina. — These  are  known  collectively  as 
the  kerqphyllous  tissue,  and  clothing  the  inner  sur- 
face of  the  wall  dovetail  with  the  sensitive  laminae 


352      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 


like  interlocking  leaves  of  two  books.  Each  lamina 
extends  approximately  from  the  upper  and  inner 
margin  of  the  hoof  to  its  plantar  border.  There 
are  from  five  to  six  hundred  of  these  laminae  in  each 
foot  and  they  all  increase  in  width  from  above  to 
below.  In  a  horizontal  section  of  the  hoof  these 
laminae  appear  like  so  many  papillae  (Fig.  2480). 

From  such  a  sec- 
tion it  will  be  seen 
that  along  the 
sides  of  each  lam- 
ina there  are  about 
sixty  secondary 
folds,  called  lamel- 
la, by  which  the 
surf  ace  between 
sensitive  and  in- 
sensitive laminae 

is     enormOUSlv    Itt- 

creased.  These 
secondary  leaves 
establish  a  fine  se- 
ries of  longitudinal 
grooves  along  the 
lateral  sides  of 
each  lamina,  as 
seen  in  Fig.  2486. 
The  surface  lining 
of  each  horny  fold 

consists  of  a  single  layer  of  cubical  or  low  colum- 
nar epithelial  cells  analogous  and  continuous  with 
the  germinal  layer  of  the  skin.  The  cells  are  rich 


Horn  tubes,  epi- 
thelial cells. 

Horn  matrix,  epi- 
thelial cells. 


Insensitive  lamina, 
epithelial  tissue. 


Secondary  lamina  or 
lamella  lined  by 
malpighian  layer  of 
epithelial  cells. 


Sensitive  lamina  con- 
nective  tissue. 


Blood-vessel. 


Fig.  2480. — Horizontal  section  of  hoof  of 
horse. 


THE:  SKIN. 


353 


in  chromatin  and  are  doubtless  capable  of  active 
multiplication.  A  few  scaly  epithelial  cells  are 
always  found  in  the  body  of  each  lamella,  but  in 
the  substance  of  each  lamina  the  tissue  appears 
to  be  compact  and  of  a  fibrous  variety.  It  is  this 
compact  tissue  that  is  called  collectively  the  insen- 
sitive lamina.  This  fibrous  tissue  can  be  traced 
outward  to  the  bases  of  the  laminae,  where  it  mingles 
with  and  is  ultimately  lost  in  the  epithelial  horn 
wall  of  the  hoof.  While  nuclei  are  absent,  the 
tissue  should  be  regarded  as  made  up  of  scaly  epi- 

Horny  tubes  and  wall  matrix. 


Secondary  laminae  or  lamella. 

Fig.  2486. — Diagram  of  horizontal  section  through  wall  of  hoof. 

thelial  plates  so  arranged  as  to  give  it  a  fibrous  ap- 
pearance very  similar  to  the  stratum  lucidum  of  the 
human  skin. 

Vascular  Lamina. — These  structures,  collectively 
known  as  the  podophyllous  tissue,  are  leaf-like 
growths  of  the  dermis,  which  interlock  very  snugly 
with  the  horny  laminae  and  lamellae  just  described. 
They  form  an  expansive  fibrous  and  vascular  tissue 
uniting  the  distal  phalanx  with  the  horny  epidermal 
laminae  of  the  hoof.  They  are  also  called  the  sensi- 
tive lamina,  and,  while  the  nerve  endings  in  them  have 
23 


354      NORMAL   HISTOLOGY   AND  ORGANOGRAPHY. 

not  been  worked  out  very  carefully,  it  is  reasonable 
to  suppose  that  we  have  much  the  same  structure  as 
in  the  human  nail-bed,  such  as  free  nerve  endings, 
end-bulbs,  and  perhaps  Rufini  corpuscles. 

Hoof  Horn. — Like  bone,  this  is  tubular,  re- 
sembling Haversian  systems,  but,  unlike  bone,  it 
consists  of  compact  layers  of  epithelial  cells.  As  the 
human  nail  develops  from  the  germinal  epithelium 
at  the  root  of  the  nail,  so  the  wall  of  the  hoof  de- 
velops from  similar  epithelium  that  covers  the 
coronary  cushion  situated  at  the  upper  margin  of 
the  hoof  wall.  This  cushion  has  an  abundance  of 
epithelial  papillae,  and  from  the  surface  of  these 
papillae  cells  proliferate  to  form  the  wall  of  the  hoof 
tubes,  while  from  the  epithelium  at  the  bases  of 
these  papillae  cells  proliferate  to  form  the  hoof  matrix. 
Thus,  the  hoof  horn  is  exclusively  an  epithelial  tissue, 
composed  of  flattened,  scaly  cells,  with  often  an 
easily  detected  nucleus,  cemented  together  com- 
pactly, their  protoplasm  being  replaced  by  keratin 
granules,  a  protein-like  substance  very  insoluble  and 
containing  4.23  per  cent,  sulphur.  The  horn  tubes 
extend  downward  from  the  papillae  of  the  coronary 
cushion  and  are  parallel  to  each  other.  These  tubes 
are  smaller  near  the  surface  of  the  hoof  and  become 
larger  in  the  deeper  portion.  The  scaly  cells  of  the 
tube  wall  are  placed  with  their  flat  surfaces  facing 
the  tubes,  that  is,  their  long  axes  are  perpendicular, 
while  the  long  axis  of  the  matrix  cells  are  horizontal. 
This  conforms  to  their  origin,  the  former  prolifer- 
ating from  the  sides  of  the  vertical  coronary  papillae, 
while  the  latter  come  from  the  horizontal  coronary 


THE  SKIN.  355 

surface  between  the  bases  of  these  papillae.  Frag- 
ments of  epithelial  cells  may  usually  be  found  in  the 
lumen  of  these  tubes. 

The  laminae  just  described  provide  an  enormous 
surface  of  contact  between  the  inner  face  of  the  wall 
and  the  external  surface  of  the  pedal  bone.  It  is 
estimated  that  this  surface  is  equal  in  area  to  eight 
or  ten  square  feet  in  each  hoof,  and  its  chief  function 
is  doubtless  to  furnish  support  to  the  body  weight 
of  the  horse.  The  sensitive  laminae  thus  act  as  an 
extensive  and  delicate  cushion,  tempering  the  jar 
sustained  in  walking  or  running.  An  inflammation 
of  the  sensitive  laminae  is  known  as  laminitis,  a 
malady  not  uncommon  in  the  horse. 

The  normal  growth  of  the  hoof  is  estimated  at  nearly 
one-half  inch  a  month.  Just  how  the  horny  laminae 
move  imperceptibly  downward  past  the  softer  lami- 
nated structure  is  a  subject  of  much  speculation  among 
veterinarians,  but  one  on  which  opinions  differ.  It 
seems  to  me  any  sliding  process  is  difficult  to  explain 
and  that  the  solution  sought  is  one  of  cell  growth. 
During  embryonic  development  it  is  easy  to  conceive 
of  a  rapid  multiplication  of  the  germinal  epithelium, 
that  is,  the  cells  that  form  the  membrane  clothing  the 
insensitive  laminae.  Such  a  growth  produces  lateral 
pressure  and  accounts  for  the  extensive  folding  of  these 
laminated  structures.  In  the  adult  foot  the  cells  of 
the  germinal  layer  show  nuclei  rich  in  chromatin, 
and  being  epithelial  cells  their  multiplication  con- 
tinues through  life.  The  horny  laminae,  lying  exter- 
nal to  this  layer,  doubtless  owe  their  origin,  as  well 
as  their  constant  and  regular  growth,  to  the  cells  of 


356      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

the  germinal  epithelium.  In  fact,  embryologically 
this  layer  is  to  be  considered  as  a  part  of  the  horny 
laminae  rather  than  interposed  between  the  horny 
and  the  soft  laminae,  as  is  done  by  most  authors. 
The  hoof  wall,  on  the  other  hand,  grows  exclusively 
from  the  epithelial  surface  of  the  coronary  cushion, 
and  its  downward  progress  is  synchronous  and  uni- 
form with  the  growth  of  the  horny  laminae,  as  de- 
scribed above.  The  provisional  horn  that  appears 
after  removing  a  part  of  the  hoof  wall,  surgically  or 
otherwise,  is  explained  as  a  cell  proliferation  of  the 
germinal  epithelium.  If  the  human  nail  is  removed 
this  germinal  epithelium  is  torn,  but  enough  remains 
to  proliferate  epithelial  cells  in  a  few  days  which  cor- 
nify  to  form  a  thin  provisional  nail  analogous  to  the 
provisional  hoof  in  a  like  injury  to  the  horse's  foot. 

THE  GLANDS  OF  THE  SKIN. 

Sweat  glands  are  coiled  simple  tubular  glands  dis- 
tributed over  the  whole  surface  of  the  skin,  with  the 
exception  of  the  inner  surface  of  the  prepuce,  the 
glans  penis,  and  the  red  borders  of  the  lips.  In  the 
axilla  and  around  the  anal  opening  they  are  excep- 
tionally large  and  often  branched.  They  are  most 
numerous  on  the  palm  of  the  hand  and  the  sole  of 
the  foot,  where  they  number  two  thousand  seven 
hundred  to  the  square  inch.  On  the  forehead  there 
are  one  thousand  two  hundred,  and  on  the  cheek 
about  five  hundred  to  the  square  inch,  while  over  the 
back  they  are  the  least  numerous.  Their  total  num- 
ber over  the  whole  body  has  been  estimated  at  nearly 
two  million  four  hundred  thousand,  which,  with  an 


SKIN. 


357 


average  length  of  three-fourths  of  an  inch,  makes 
the  united  length  approximately  twenty-eight  miles. 
This  vast  secreting  surface  is  constantly  secreting 
moisture,  either  as  insensible  or  sensible  perspiration. 
The  amount  of  this  perspiration  within  a  given  time 


Fig.  249. — Under  surface  of  the  epidermis,  separated  from  the  cutis 
by  boiling.  The  sweat  glands  may  be  traced  for  a  considerable  part 
of  their  length;  a,  Sweat  gland  ;  b,  longitudinal  ridge;  c,  depression, 
d,  cross  ridge  (Bohm  and  Davidoff). 


varies  considerably,  but  in  the  average  person  in 
good  health  it  is  estimated  at  about  two  pints  every 
twenty-four  hours. 

The  excretory  ducts  open  on  the  surface  of  the 
skin  by  numerous  sweat  pores  along  the  crests  of  the 
epidermal  ridges.  These  pores  may  be  seen  with  a 
low  magnification  or  ordinary  hand  lens.  The  duct 
is  spirally  twisted  in  the  stratum  corneum  and  enters 
the  dermis  between  two  dermal  papillae;  that  is,  at 
the  apex  of  an  epidermal  papilla.  In  the  dermis  it 
takes  a  sinuous  or  nearly  straight  course  and  pene- 


358     NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 


trates  to  the  lower  stratum  of  the  skin,  or  even  deeper, 
to  the  subcutaneous  connective  tissue.  This  distal 
end  is  very  much  coiled  and  constitutes  the  secreting 
portion  of  the  gland.  In  the  epidermis  the  duct  has 
no  other  wall  than  the  epithelial  cells  of  the  various 
layers  through  which  it  passes,  but  in  the  dermis  the 
wall  is  composed  of  a  single  layer  of  short  cubical  cells 
outside  of  which  there  is  a  delicate  basement  mem- 
brane. The  secreting 
portion  is  also  lined  by 
simple  epithelium,  but 
the  cells  are  larger  and 
have  a  finely  granular 
protoplasm.  Between  the 
gland  cells  and  the  base- 


250. — Cross  section  of  deep 
portion  of  sweat  gland. 


ment  membrane  there 
is  found  in  the  larger 
glands,  a  single  layer  of 
non-striated  muscle  cells  arranged  longitudinally. 
This  muscle  is  derived  from  the  ectoderm,  while  the 
other  musculature  of  the  body  comes  from  the  meso- 
derm.  The  muscle  of  the  sweat  glands  probably 
aids  these  glands  in  expelling  their  products  of  secre- 
tion. Non-medullated  nerve  fibers  of  the  sympa- 
thetic system  form  a  delicate  network  just  external 
to  the  basement  membrane  called  the  epilamellar 
plexus.  From  this  plexus  delicate  fibers  pass 
through  the  basement  membrane  to  ramify  between 
the  gland  cells,  where  they  end  in  clusters  of  small 
terminal  granules.  The  physiological  activities  of 
the  sweat  glands  are  thus  directly  under  the  control 
of  the  nervous  system  and  do  not  depend  on  the 


SKIN.  359 

blood  supply,  a  fact  that  may  also  be  demonstrated 
by  physiological  experiments. 

Sebaceous  glands  are  associated  with  hair  follicles, 
into  which  they  pour  their  contents.  They  are  also 
found  on  the  red  borders  of  lips,  the  labia  minora, 
the  glans  and  prepuce,  where  hairs  are  absent. 
They  are  simple  branched  alveolar  glands  that  se- 
crete an  oily  substance  called  sebum.  This  is  a 


Hair  follicle. 


Hair  follicle. 


Fig.  251. — Model  of  a  sebaceous  gland  with  a  portion  of   the  hair 
follicle,  reconstructed  by  Bern's  wax-plate  method  (Huber). 

fluid  at  the  temperature  of  the  body,  keeps  the  skin 
soft  and  flexible,  and  also  supplies  a  natural  dressing 
for  the  hair.  In  the  scalp  there  may  be  ah  exces- 
sive secretion  of  sebum  which  dries  and  exfoliates 
with  the  horny  epidermis  as  dandruff. 

Each  hair  follicle  has  two  or  more  sebaceous 


NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


Fig.   252. — Section  of  two  alveoli  of  a 
sebaceous  gland. 


glands  that  vary  in  size  from  0.2  to  0.5  mm.  The 
excretory  duct  is  short  and  wide  and  opens  into  the 
upper  third  of  the  follicle.  This  duct  is  lined  by 
stratified  epithelium  that  is  directly  continuous  with 

the  outer  root 
sheath  of  the  hair 
follicle.  The  cells  of 
the  alveoli  are  very 
large  and  contain  fat 
globules  that  vary 
in  size  and  give  a 
reticular  appearance 
to  the  cytoplasm. 
The  nuclei  are  rela- 
tively small.  The 
cells  completely  fill 

the  alveoli  so  that  the  latter  appears  to  be  solid. 
The  cells  disintegrate  and  change  directly  into  secre- 
tion, which  is  then  poured  into  the  follicle  as  sebum. 
The  renewal  of  lost  cells  takes  place  by  constant 
proliferation  of  basal  cells.. 

It  is  quite  common  in  the  scalp  to  find  sebaceous 
cysts,  or  wens,  which  result  from  an  occlusion  of  the 
duct  and  an  enlargement  of  the  gland.  These  cysts 
are  lined  by  a  simple  layer  of  epithelium  and  fillec 
with  a  white,  waxy,  or  semisolid  fluid  quite  analo- 
gous to  the  sebum.  Wens  are  of  slow  growth  anc 
cause  no  disturbance,  unless  they  get  very  large  or 
become  infected  by  being  carelessly  opened.  The 
radical  cure  consists  in  their  complete  removal,  in- 
cluding the  epithelial  wall. 


CHAPTER  XI. 
PERIPHERAL  NERVE  TERMINATIONS. 

Physiologically,  nerve  endings  may  be  classified  as 
motor  or  sensory. 

MOTOR  NERVE  ENDINGS* 

(The  Telodendria  of  Nerve  Fibers  in  Muscle  Tissue.) 

i .  In  Striated  Muscle. — The  nerve  endings  in  stri- 
ated muscle  are  called  muscle-end  plates,  or  sole  plates. 
In  the  higher  vertebrates  these  are  found  in  the 
muscle  sarcoplasm  just  beneath  the  sarcolemma  of 
each  muscle  fiber.  A  motor  nerve  fiber  as  it  ap- 
proaches its  termination  becomes  much  branched 
so  as  to  innervate  from  ten  to  twenty  muscle  fibers. 
The  axis  cylinder  enters  the  sarcoplasm  where  it  im- 
mediately terminates  in  a  web-like,  flat  end-brush  with 
numerous  dilatations.  The  axilemma,  or  Henle's 
sheath,  is  continuous  around  the  brush.  The  me- 
dullary layer  stops  short  at  the  level  of  the  sarco- 
lemma; that  is,  at  the  surface  of  the  sarcoplasm. 
The  neurolemma  is  continuous  with  the  sarcolemma 
of  the  muscle  fiber.  The  adjacent  sarcoplasm  of  the 
muscle  fiber  is  granular  and  a  liberal  supply  of  muscle 
nuclei  is  also  present  in  the  proximity,  which  results 
in  an  elevation  of  the  muscle  fiber  at  the  point  of 
nerve  contact  known  as  Doyer's  elevation. 


362      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

2.  In  non-striated  and  in  heart  muscle  the  nerve 
termination  is  more  simple.  The  muscle  is  supplied 
with  neurons  from  the  sympathetic  system,  most  of 
which  are  of  the  non-medullated  variety.  These 
fibers  branch  repeatedly  to  form  an  extensive 


Nerve-end 
brush. 

So-called  gran- 
ular sole. 


—  Muscle  fiber. 


Fig.  253. — Motor  endings  in  striated  voluntary  muscles.  From 
Pseudopus  Pallasii.  As  a  consequence  of  the  treatment  the  arborescence 
is  shrunken  and  interrupted  in  its  continuity.  The  end  plate  is  in  con- 
nection with  two  nerve  branches  (Bohm  and  Davidoff). 

primary  plexus  surrounding  the  muscle  bundles. 
From  this  plexus  non-medullated  fibers,  that  is, 
just  the.as^s  cylinders,  penetrate  the  heart  muscle, 
or  the  involuntary  muscle,  where  they  anastomose 
to  form  a  delicate  secondary  plexus,  from  which  lat- 
eral short  twigs  pass  to  end  in  minute  dilatations  or 
granules  upon  the  muscle  cells. 


PERIPHERAL  NERVE  TERMINATIONS. 


363 


SENSORY  NERVE  ENDINGS. 
(Telodendria  of  Dendrites.) 

The  sensory  nerve  terminations  are  essentially 
the  terminals  of  dendrites  as  distinguished  from  the 
motor  plates  which  are  the  terminals  of  axones. 
The  cell  bodies  of  these  sensory  neurons  are  found 
in  the  spinal  and  cranial  ganglia,  often  at  a  consid- 
erable distance  from  the  sensory  termination.  In 


1 

$ 


Fig.  254. — Motor  nerve  ending  on 
heart  muscle  cells  of  cat;  methylene- 
blue  stain  (Huber,  De  Witt). 


Fig.  255. — Motor  nerve 
ending  on  involuntary  non- 
striated  muscle  cell  from 
intestine  of  cat;  methy- 
lene-blue  stain  (Huber, 
De  Witt). 


this  case  the  dendrite  is  a  long  one,  medullated,  and 
structurally  identical  with  an  axis  cylinder  or  axone. 
The  nerve  impulse  is,  however,  normally  carried 
toward  the  nerve  cell,  while  in  axones  the  impulse 
goes  the  opposite  way.  As  stated  in  another  place, 
such  sensory  neurons  have  a  long  dendrite  that  ex- 
tends peripherally  and  -a  short  axone  that  passes 
centrally;  that  is,  to  the  spinal  cord  or  brain. 


364      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

These  sensory  endings  form  telodendria  or  end- 
brushes  that  vary  in  complexity  according  to  the 
tissue  elements  that  take  part  in  their  formation. 

i.  Free  Sensory  Nerve  Endings. — These  are  the 
simplest  forms  of  nerve  endings  and  occur  in  epi- 


•  Stratum 
corneum. 


Nerve  fibers 
in  the  epi- 
dermis. 

Stratum 
Malpighii. 


I  L  «  Papilla. 


.   Nerve  fiber. 


Fig.  256. — Nerves  of   epidermis  and  papilUe  from  ball  of    cat's  foot 
(Bohm  and  Davidoff). 


thelial  tissues  and  in  some  parts  of  the  connective 
tissues.  The  sensory  nerve  fibers  near  its  termina- 
tion repeatedly  branch,  the  latter  retaining  the 
medullary  sheath.  The  branches  appear  always  at 
the  nodes  of  Ranvier.  From  this  coarse  plexus  a 


PERIPHERAL  NERVE  TERMINATIONS. 


365 


finer  non-medullated  system  of  branches  appear 
which  innervate  the  epithelium  and  terminate  in 
varicosities,  discs,  or  minute  granules  that  lie  in  appo- 
sition to  epithelial 
cells.  Similar  free 
terminations  occur 
in  tendons,  and  liga- 


Connective '-tissue 
capsule. 


Fig.  257. — Tactile  cells  from  the  bill  of  a 
duck. 


Nerve  fiber. 
__  Epithelial  cells. 

ments,  and  other 
fi  b  r  o  u  s  connective 
tissue. 

2.  Tactile  Cells. — These  are  also  called  Grandry's 
corpuscles,  and   may   be   found   in   the  duck's  bill 

just  beneath  the 
gum  epithelium. 
The  cells  are  of 
epithelial  origin, 
oval,  and  meas- 
ure about  50 //in 
diameter.  One 
to  five  cells  are 
surrounded  by  a 
connective-tis- 
sue capsule. 
These  cells  are 
superposed  on 
each  other,  with 
their  long  axes 
always  parallel 
to  the  surface  of 
the  bill.  A  me- 

dullated    nerve   fiber  may   be   traced   to  the  cap- 
sule, which  it  penetrates  and  then  becomes  non- 


-  Nucleus  of  lamellae. 


End-cell  of  core. 
Lamellae. 

Axis-cylinder  in  core. 
Cubic  cells  of  core. 

Termination  of  medul- 
lary sheath. 


•— —  Axis-cylinder  of 
nerve-fiber. 

— —   Medullary  sheath  of 

nerve-fiber. 

Neurilemma  and  sheath, 
of  Henle. 


Fig.  258. — Corpuscle  of  Herbst  from  bill  of 
duck  (Bohm  and  Davidoff). 


366     NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 


medullated.  The  latter  terminates  in  tactile  discs 
that  are  interposed  between  the  tactile  cells.  A 
group  of  three  cells  will  have  two  discs ;  five  cells 
will  have  three  discs. 

3.  Corpuscles  of  Herbst. — These  are  much  larger 

bodies  and  may  also 
be  found  in  the  bills 
of  aquatic  birds,  in 
close  association 
with  the  tactile  cells 
just  described. 
They  are  ovoid 
bodies  75^  wide  and 
150  p.  long.  There 
is  an  inner  core  sur- 
rounded with  con- 
nective-tissue lamel- 
lae. The  core  con- 
tains the  axis  cylin- 
der, which  is  thick- 
ened at  the  end  and 
is  encased  between 
two  rows  of  cells  that 
seem  to  have  the 
same  function  as 
Grandry's  corpus- 
cles .  The  nerve  fiber 

enters  at  the  end  of  the  corpuscle  and  becomes 
non-medullated  only  after  reaching  the  inner  core. 

4.  Meissner's  Corpuscles. — These  are  found  beneath 
the  epidermis  of  man,  particularly  of  the  hand  and 
foot,  and  occupy  the  dermal  papillae  of  the  dermis. 


Fig.  259. — Meissner's  tactile  corpus- 
cle; methylene-blue  stain  (Dogiel,  "In- 
ternat.  Monatsschr.  f.  Anat.  u.  Phys.," 
vol.  ix). 


PERIPHERAL  NERVE  TERMINATIONS. 


367 


They  are  oval  bodies  and  approximately  the  same 
size  as  the  corpuscles  of  Herbst.  There  is  a  thin 
connective-tissue  capsule  and  a  loose  complex  core. 
One  or  more  medullated  nerve  fibers  enter  at  the 
lower  end  of  the  corpuscle.  These  soon  become 
non-medullated  and  their  axones  then  make  a  vari- 
able number  of  spiral  turns  which  interlace,  branch, 
and  are  beset  with 
many  granules  or 
varicosities.  One 
or  more  axis  cyl- 
inders occupy  the 
center  of  the  core. 
5.  Genital  Cor- 
puscles.—  These 
are  oval  or  round 
bodies  located  in 
the  mucosa,  just 
beneath  the  epi- 
thelium of  male 
and  female  geni- 
talia.  Their  size 
varies  from  o.i 
mm.  to  0.4  mm. 
They  are  sur- 
rounded by  a  thick  fibrous  capsule  and  each  cor- 
puscle is  innervated  by  one  to  ten  medullated  nerve 
fibers.  The  latter  become  non-medullated  after 
passing  through  the  capsule,  and  the  axones  then 
form  a  complex  core  quite  analogous  to  that  of 
Meissner's  corpuscle.  In  fact,  the  two  are  very 
similar  structures. 


Fig.  260. — Genital  corpuscle  from  the 
glans  penis  of  man;  methylene-blue  stain 
(Dogiel,"Arch.  f.  mik.  Anat.,"  vol.  XLI.) 


Lamella. 


Granular  cove. 


Axis  cylinder 


Fig.  261. — Pacinian  corpuscle  from  mesentery. 


Fig.  262. — Neuromuscular  nerve-end  organ  from  the  intrinsic  plantar 
muscles  of  dog;  from  teased  preparation  of  tissue  stained  in  methylene- 
blue.  The  figure  shows  the  intrafusal  muscle  fibers,  the  nerve  fibers  and 
their  terminations;  the  capsule  and  the  sheath  of  Henle  are  not  shown 
(Huber  and  De  Witt,  "Jour.  Comp.  Neurol.,"  vol.  vn). 


PERIPHERAL   NERVE  TERMINATIONS. 


369 


6.  Pacinian  Corpuscles. — These  are  oval  bodies 
and  the   larger   ones  are  easily 

visible  to  the  naked  eye,  being 
over  2  mm.  long.  Structurally 
they  seem  related  to  the  corpus- 
cles of  Herbst.  They  are  found 
in  the  dermis  of  the  hand  and 
foot,  particularly  along  the  lower 
surface  of  the  fingers  and  toes. 
They  are  also  found  in  the  joints, 
the  peritoneum,  pleura,  pericar- 
dium, and  are  especially  abun- 
dant in  the  mesentery.  The 
greater  portion  of  the  corpuscle 
consists  of  concentric  lamellae  of 
connective-tissue  origin.  B  e- 
tween  these  flat  endothelial  cells 
intervene.  A  granular  core 
forms  the  axis  of  the  corpuscle, 
in  the  center  of  which  the  axis 
cylinder  maybe  traced.  Usually 
one  large  nerve  fiber  goes  to  each 
corpuscle.  After  entering  the 
core  this  forms  a  plexus  of  fine 
branches  and  becomes  non-med- 
ullated. 

7.  Tendon  and  Muscle    Spin- 
dles.— A  tendon  spindle  is  an  ex- 
pansion of   tendon  bundles  en- 
closed in  a  well  defined  connec- 
tive-tissue   sheath.     The    nerve 

fiber  enters  the  middle  of  the  spindle,  divides  re- 

24 


Fig.  263.— Neuroten- 
dinous  nerve-end  organ 
from  rabbit ;  teased 
preparation  of  tissue 
stained  in  methylene- 
blue  (Huber  and  De 
Witt,  "Jour.  Comp. 
Neurol.,"  vol.  x). 


370      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

peatedly,  becomes  non-medullated  and  finally  ter- 
minates in  varicosities  or  expanded  clavate  ends. 
The  muscle  spindle  is  a  collection  of  delicate  muscle 
fibers  enveloped  in  a  dense  perimysium  sheath,  the 
whole  being  innervated  by  sensory  nerve  endings 
much  as  in  tendon  spindles.  The  sensory  endings 
both  in  tendon  and  muscle  transmit  the  sensation 
of  tension  which  becomes  the  basis  for  coordinate 
movements. 


CHAPTER  XII. 
THE  SPINAL  CORD. 

The  spinal  cord  is  an  organ  composed  largely  of 
neurons,  with  which  are  associated  blood-vessels, 
connective-tissue  elements,  and  a  limited  amount  of 
epithelial  and  muscle  cells.  It  represents  the  ter- 
minal portion  of  the  cerebrospinal  axis  and  is  a 
direct  continuation  of  the  encephalon.  It  is  one  of 
the  first  organs  to  develop  in  the  embryo  where  it 
makes  its  appearance  as  a  dorsal  ectodermal  groove. 
This  neural  groove  gradually  closes  to  form  a  canal 
which  lies  at  first  just  beneath  the  ectoderm  and 
later  becomes  encased  in  connective-tissue  layers  and 
the  bony  axial  skeleton. 

The  cord  is  bilaterally  symmetrical  and  flattened 
dorso-ventrally.  It  presents  two  enlargements: 

(1)  the  upper  or  cervical,  which  extends  from  the 
third  cervical  vertebra  to  the  second  thoracic  and 
corresponds  to  the  origin  of  the  nerves  of  the  arm,  and 

(2)  the  lower  or  lumbar,  which  extends  from  the 
ninth  thoracic  vertebra  to  the  terminal  cone  at  the 
level  of  the  body  of  the  second  lumbar  vertebra. 
The  lumbar  enlargement  marks  the  origin  of  the 
nerves  of  the  leg.     From  the  apex  of  the  terminal 
cone  there  extends  a  slender  rudimentary  prolonga- 
tion,  the   filum   terminate,   which,   with  the   spinal 
nerves  of  this  region,  is  called  the  cauda  equina.    The 


372      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

spinal  cord,  therefore,  does  not  extend  the  whole 
length  of  the  vertebral  canal  but  only  to  the  level  of 
the  second  lumbar  vertebra.  Its  length  is  about 
eighteen  inches,  its  diameter  one-half  inch  or  less. 
Membranes  of  the  Cord  or  Meninges. — i.  The 
Dura. — This  is  a  thick  strong  membrane  composed  of 


Blood  capillaries  in  white  matter. 


Spinal 
ganglion 


Posterior  root  of  spinal  nerve 


Ligamentum 
denticulatum. 

A  nterior  root  of  ' 
spinal  nerve. 


Posterior  root. 
Anterior  root. 
Dorsal  spinal 

ganglion. 
Dura  mater. 


Arachnoid. 


Pia  mater. 


Blood-vessels. 
Fig.  264. — Portion  of  spinal  cord  and  membranes  dissected 

white  fibrous  tissue  which  forms  the  outer  covering 
of  the  cord.  Many  blood-vessels  find  lodgment  in 
this  membrane.  It  is  analogous  and  continuous 
with  the  dura  of  the  brain,  the  most  striking  differ- 
ence being  that  the  dura  of  the  cord  does  not  form 


THE  SPINE.  273 

the  internal  periosteum  of  the  vertebral  canal.  Be- 
tween the  dura  and  the  vertebrae  is  a  space  called 
the  epidural  space,  which  is  filled  with  areolar  tissue, 
fat,  and  a  plexus  of  spinal  veins. 

2.  The    Pia. — This    is    a    thin    connective-tissue 
layer  that  lies  close  to  the  surface  of  the  cord,  dips 
into  the  anterior  fissure,  and  also  sends  fibers  or 
trabeculae   into   the   cord  substance.     Many  small 
blood-vessels  accompany  this  layer. 

3.  The  Arachnoid. — This  is  a  delicate  membrane 
between  the  other  two,  but  much  nearer  the  dura. 
Its  external  surface  is  clothed  with  a  single  layer 
of  flat  epithelial  cells  which  secrete  a  serous  fluid. 
The  arachnoid  is  therefore  a  serous  membrane. 

Fissures. — i.  Posterior  Median  Fissure. — This  is  a 
median  dorsal  fissure  that  extends  the  whole  length 
of  the  cord.  It  is  extremely  narrow  but  deep,  as  it 
'penetrates  to  the  central  gray  matter,  being  inti- 
mately connected  with  the  two  sides  in  its  course. 
The  single  septum  is  derived  from  the  neuroglia  tis- 
sue, and  not  from  the  pia,  which  sends  no  prolonga- 
tion of  any  kind  into  it. 

2.  Anterior  Median  Fissure. — This  also  extends 
the  whole  length  of  the  cord.     It  is  shallower  but 
wider  than  the  posterior  fissure  and  does  not  quite 
reach  the  central  gray  matter.     The  pia  forms  a 
fold  into  this  fissure  with  which  is  associated  many 
blood-vessels.     The  two  median  fissures  or  clefts 
divide  the  cord  into  a  right  and  a  left  half,  each 
practically  identical  with  the  other. 

3.  Poster o-lateral  Groove.— This  is  a  shallow  de- 
pression on  each  side  of  the  posterior  fissure  and 


374    NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

marks  the  entrance  into  the  cord  of  the  dorsal  roots 
of  the  spinal  nerves.  In  a  like  position,  anteriorly, 
is  the  exit  of  the  anterior  roots  of  the  spinal  nerves, 
but  there  is  no  depression  or  groove  as  in  the  case  of 
the  posterior  roots.  The  two  roots  of  the  spinal 
nerves  divide  each  half  of  the  spinal  cord  into  three 
regions  or  major  tracts  known  as  the  posterior, 


tferior     horn 
ell. 

issed  Pyram- 
ial  column. 
Igi     cell     of 
osterior  horn, 
red     cerebel- 
ir  column. 
Column  cells. 
Igi's  commis- 
ural  cells, 
'ers's  column. 


Motor  cells.  — 


Collate? 
of  en 
Pyra, 
colun 


Collatet 
endin 
the  gi 
matte 


Direct  Pyramidal  column. 

Fig.  265. — Schematic  diagram  of  the  spinal  cord  in  cross  section  after 
von  Lenhossek,  showing  in  the  left  half  the  cells  of  the  gray  matter,  in 
the  right  half  the  collateral  branches  ending  in  the  gray  matter  (Huber). 


lateral,  and  anterior  columns.  The  posterior  column 
is  limited  by  the  posterior  fissure  and  the  posterior 
roots,  the  lateral  is  the  region  between  the  roots, 
and  the  anterior  lies  between  the  anterior  root  and 
the  anterior  fissure. 

Spinal  Neryes. — Thirty-one  pairs  of  nerves  arise 
from  the  side  of  the  cord.     These  are  classified  into 


THE  SPINE.  375 

8  cervical,  12  dorsal,  5  lumbar,  5  sacral,  and  i  coc- 
cygeal.  Each  nerve  is  attached  to  the  cord  by  a 
dorsal  and  a  ventral  root.  Each  root,  before  uniting 
with  the  cord,  breaks  up  into  secondary  bundles  and 
spreads  out  like  a  fan,  making  a  continuous  linear 
attachment.  The  dorsal  ganglion  is  located  upon 
the  dorsal  within  the  vertebral  canal,  near  the  union 
of  the  two  roots. 

Gray  Matter  of  the  Cord. — The  gray  matter  of  the 
cord  is  centrally  located  and  takes  the  form  of  a 
capital  letter  H.  The  gray  matter  in  each  lateral 
half  resembles  a  crescent  which  is  joined  to  the  op- 
posite side  by  an  isthmus,  in  the  center  of  which  is 
the  central  canal.  The  latter  is  usually  obliterated 
in  the  adult  man,  and  is  filled  as  well  as  surrounded 
by  the  gelatinous  substance  of  Rolando,  which  is  a 
reticular  structure.  That  part  of  the  isthmus  above 
the  central  canal  is  called  the  posterior  gray  com- 
missure, while  the  gray  matter  ventral  to  the  canal 
is  the  anterior  commissure. 

Each  crescent  may  be  divided  into  a  posterior, 
lateral,  and  anterior  horn.  The  anterior  horn  is  the 
largest  and  the  lateral  horn  is  the  smallest.  The 
posterior  horn  is  pointed  and  approaches  near  to  the 
posterior  lateral  groove.  The  apex  of  this  horn  is 
called  the  zona  terminalis.  At  the  base  of  this  apex 
there  is  a  reticular  substance  called  the  zona  reticu- 
laris,  while  next  to  this  and  apparently  capping  the 
posterior  horn  is  a  gelatinous  mass,  similar  to  that 
which  surrounds  the  central  canal,  called  the  sub- 
stantia  gelatinosa  of  Rolando. 

The  nerve  cells  of  the  posterior  horn  are  irregularly 


376 


NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


distributed  and  some  of  them  are  particularly  small 
and  have  a  stellate  appearance.  At  the  base  and 
mesial  surface  of  this  horn  there  is  a  group  of  large 
nerve  cells  called  the  column  of  Clarke.  This  column 
extends  from  the  second  lumbar  up  through  the 
dorsal  region  of  the  cord  to  the  cervical.  In  the 
cervical  region  it  is  absent;  however,  Sailing's  nu- 
cleus of  this  region  may  represent  a  remnant  of  the 
column  of  Clarke.  At  the  base  of  the  dorsal  horn, 
deeper  down  and  lateral  to  Clarke's  column,  another 
group  of  nerve  cells  may  be  found  that  is  called 
Waldeyer's  central  cell  column.  This  is  reciprocal 
with  Clarke's  column;  that  is,  in  the  dorsal  region 
where  Clarke's  column  is  conspicuous,  only  rem- 
nants of  Waldeyer's  tract  can  be  found,  while  in  the 
other  regions  of  the  cord  this  cell  tract  is  particu- 
larly prominent. 

The  lateral  horn  is  a  small  lateral  prominence  at 
the  side  of  the  gray  crescent.  In  the  substance  of 
this,  a  small  collection  of  nerve  cells  may  be  found, 
while  just  beneath  this  the  gray  matter  cuts  into 
the  white  matter,  forming  processes  called  the 
processus  reticularis. 

The  anterior  horn  is  not  only  large  but  presents  a 
blunt,  rounded  appearance.  The  nerve  cells  of  this 
horn  are  very  large  and  have  been  classified  according 
to  their  position  into  antero-mesial,  postero-mesial, 
antero-lateral,  and  postero-lateral.  The  axis  cylin- 
der of  most  of  these  cell  bodies  goes  to  form  the  an- 
terior root  of  the  spinal  nerves.  They  therefore 
carry  only  motor  impulses. 

White  Matter  of  the  Cord.— The  white  matter  of 


THE   SPINE. 


377 


the  cord  consists  of  medullated  nerve  fibers.  Most  of 
these  fibers  have  no  neurilemma,  and  the  cord  there- 
fore is  soft  and  pulpy,  in  contrast  to  the  nerve 
trunks  whose  fibers  have  a  neurilemma  which  with 
the  connective-tissue  elements  make  nerves  tough 
and  strong.  The  white  matter  practically  encloses 
the  gray.  The  fibers  which  compose  it  vary  con- 


Postero-lateral  horn. 


Posterior  horn.  " 


Posterior  fissure. 


Lissaur's  marginal 

ground  bundle. 
Comma  tract. 
Pia  mater. 


Direct  cerebellar 
tract. 


Cower  s's  tract. 
Processus  reticularis. 

Lowenthal's  tract. 


Anterior  commissure.    Anterior  fissure.     Direct  pyramidal  tract. 


Fig.  266. — Cross  section  of  the  spinal  cord,  dorsal  region,  i,  Zona 
terminalis;  2,  zona  reticularis;  3,  substantia  gelatinosa  of  Rolando;  4, 
stellate  cells  of  posterior  horn;  5,  column  of  Clarke;  6,  Waldeyer's 
central  cell  column;  7,  cells  of  lateral  horn;  8,  central  canal;  9,  antero- 
mesial  cells;  10,  postero-mesial  cells;  n,  antero-lateral  cells;  12,  pos- 
tero-lateral  cells. 


siderably  in  size,  both  large  and  small  being  mixed 
up  together.  In  sections  of  the  adult  healthy  cord 
no  evidence  of  definite  tracts  of  fibers  can  be  seen. 
We  know,  however,  that  longitudinally  arranged 
groups  of  fibers  run  a  definite  course,  have  definite 
connections,  and  carry  impulses  that  result  in  defi- 
nite sensations  and  actions.  The  physiological  em- 


378       NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

deuce  of  this  fact  is  experimental  and  positive.  A 
nerve  fiber  detached  from  its  cell  body  dies.  In 
this  way  tracts  will  degenerate  in  the  cord,  some 
above  and  some  below  a  transverse  cut.  The  em- 
bryological  evidence  rests  on  equally  positive  facts. 
In  development  certain  tracts  acquire  medullary 


Postero-lateral  horn.    Posterior  fissure. 


A  nterior 
horn. 


Lowenthal's 
tract. 


Anterior  root  of  spinal  nerve.          Anterior  fissure. 


Fig.  267. — Cross  section  of  the  spinal  cord,  lumbar  region,  i,  zona 
terminalis;  2,  zona  reticularis;  3,  substantia  gelatinosa  of  Rolando;  4, 
stellate  cells  of  posterior  horn;  5,  column  of  Clarke;  6,  Waldeyer's  cen- 
tral cell  column;  7,  cells  of  lateral  horn;  8,  central  canal;  9,  antero- 
mesial  cells;  10,  postero-mesial  cells;  n,  antero-lateral  cells;  12,  postero- 
lateral  cells. 

sheaths  earlier  than  others.  This  fact  has  greatly 
extended  our  knowledge  of  the  white  matter  in  the 
cord.  The  pathological  evidence  is  a  third  factor. 
Certain  diseases  produce  degenerate  lesions  in  the 
cord.  Proper  interpretations  of  these  lesions  have 
enabled  us  to  map  out  definite  nefve  tracts  in  the 
cord,  and  to  determine  their  relations  as  well  as  pos- 


379 

sible  functions.  The  information  evolved  from 
these  sources  makes  a  classification  of  tracts,  in  the 
cord,  possible. 

Tracts  of  the  Cord.— POSTERIOR  REGION. 

1 .  Column  of  Goll. — This  lies  adjacent  to  the  dorsal 
fissure  and  extends  the  whole  length  of  the  cord. 
Its  fibers  arborize  about  nerve  cells  in  the  nucleus 
gracilis  of  the  lower  region  of  the  medulla. 

2.  Column  of  Burdach. — This  extends  parallel  to 
the  column  of  Goll  between  the  latter  and  the  pos- 
terior horn  of  gray  matter.     It  extends  the  whole 
length  of  the  cord  and  its  fibers  arborize  about  nerve 
cells  in  the  nucleus  cuneatus  of  the  medulla,  adjacent 
to  the  nucleus  gracilis.     The  column  of  Goll  becomes 
wider  in  the  upper  portions  of  the  cord  and  that  of 
Burdach  narrower.     This  is  due  to  nerve  fibers  that 
gradually  pass  into  the  column  of  Goll  from  the  col- 
umn of  Burdach  on  their  way  to  the  brain. 

3.  Comma  Tract. — This  is  a  small  tract  found  in 
the   column   of   Burdach,    and    represents   sensory 
fibers  from  the  posterior  roots  of  the  spinal  nerves 
that  pass  down  the  cord  for  a  short  distance,  and 
then  turn  into  the  anterior  horn  of  gray  matter  to 
arborize  about  nerve  cells  of  this  region. 

4.  Lissaur's  Marginal  Ground  Bundle. — This  is  a 
small  commissural  tract  placed  near  the  surface  of 
the  cord  just  lateral  to  the  entrance  of  the  posterior 
root  fibers.     It  is  formed  by  some  of  the  fibers  of 
this  root.     The  tract  extends  the  whole  length  of 
the  cord,  but  each  individual  fiber  runs  but  a  short 
distance  and  then  turns  inward  to  arborize  about 
nerve  cells  of  the  posterior  horn. 


380       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

These  four  tracts  are  composed  almost  entirely  of 
nerve  fibers  that  enter  the  cord  by  the  posterior 
roots  of  the  spinal  nerves.  They  are  therefore  sen- 
sory tracts  and  forward  impulses  toward  the  brain. 
The  termination  of  the  posterier  root  fibers  may  be 
enumerated  as  follows: 

1.  Column  of  Goll,  Burdach,  comma  tract,   Lis- 
saur's  tract. 

2.  Arborize  about  the  cells  in  Clarke's  column. 

3.  Arborize  about  the  cells  in  posterior  horn. 

4.  Arborize  about  the  cells  in  anterior  horn  on 
same  and  opposite  side. 

Lateral  Region. — The  tracts  of  this  region  are:  (i) 
Direct  Cerebellar ;  (2)  Go wers's,  or  Ascending  Antero- 
lateral;  (3)  Crossed  Pyramidal;  (4)  Lowenthal's, 
or  Antero-lateral  Descending ;  (5)  Mixed  Lateral. 

1.  The  Direct  Cerebellar. — This  is  a  band  of  fibers 
that  lies  at  the  surface  of  the  cord  just  lateral  to  the 
dorso-lateral  groove.     Its  nerve  fibers  are  derived 
from  the  cells  of  the  column  of  Clarke,  consequently 
the  tract  extends  from  the  last  dorsal  up  to  the 
medulla  on  the  same  side.     It  is  an  ascending  or 
sensory  tract,  and,  as  it  is  traced  upward,  becomes 
wider  from  the  acquisition  of  axones  from  the  col- 
umn of  Clarke.     It  enters  the  cerebellum  through 
the  inferior  peduncle  and  finally  terminates  in  the 
Cerebellar  cortex  of  the  superior  worm  on  both  sides, 
chiefly  the  opposite. 

2.  Cowers' 's  tract  lies  just   in  front  of  the  direct 
Cerebellar  and  also  at  the  surface  of  the  cord.     It  is 
an  ascending  or  sensory  tract  and  some  of  its  fibers 
are  supposed  to  reach  the  cerebellum  by  passing 


THE  SPINE. 


381 


through  the  formatio  reticularis  of  the  medulla,  and 
making  a  backward  turn  through  the  superior  med- 
ullary velum  of  the  same  side. 

Other  fibers  of  this  tract  have  been  traced  to  the 
corpora  quadrigemina,  the  thalamus,  substantia 
nigra,  and  the  lenticular  nucleus  of  the  cerebrum. 
The  fibers  of  this  tract  extend  the  whole  length  of 


Posterior  roof. 


Posterior  fissure. 


Lissaur's 
marginal 
ground 
bundle. 

Comma 
tract. 

Pia  mater. 


Direct  pyramidal 
tract. 


A  tUerior  root  of  spinal  nerve. 


Anterior  fissure. 


Fig.  268.— Cross  section  of  spinal  cord  cervical  region,  i,  Zona  ter- 
minalis;  2,  zona  reticularis;  3,  substantia  gelatinosa  of  Rolando;  4, 
stellate  cells  of  posterior  horn;  5,  column  of  Clarke;  6,  Waldeyer's  cen- 
tral cell  column ;  7,  cells  of  lateral  horn;  8, 'central  canal;  9,  antero-me- 
,sial  cells;  10,^  postero-mesial  cells;  n,%antero-lateral  cells;  12,  postero- 
lateral  cells. 

the  cord  and  probably  have  "their  origin  in  the  cells 
of  the  posterior  horn. 

3.  The  crossed  pyramidal  tract  is  a  large  and 
well-defined  bundle  that  lies  just  beneath  the  direct 
cerebellar;  that  is,  between  this  and  the  posterior 
horn.  Below  the  point  where  the  direct  cerebellar 


382       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

begins,  the  crossed  pyramidal  comes  to  the  surface 
of  the  cord.  The  fibers  of  this  tract  have  their  origin 
in  the  large  pyramidal  cells  of  the  cerebrum  in  the 
region  of  the  area  of  Rolando.  Traced  downward 
from  this  source,  they  cross  in  the  lower  part  of  the 
medulla  to  the  opposite  side  of  the  cord,  making  at 
this  point  the  motor  decussation.  As  it  descends  the 
tract  gradually  diminishes  in  size,  due  to  the  fact 
that  fibers  leave  it  to  arborize  around  the  large 
motor  cells  of  the  anterior  horn.  In  this  way  the 
entire  tract  is  ultimately  exhausted  near  the  lower 
extremity  of  the  cord.  It  is  thus  a  descending  or 
motor  tract  that  governs  the  opposite  side  of  the 
body  from  where  it  has  its  origin. 

4.  LowenthaVs    tract   is    closely    associated    with 
Gowers's.     Its  position  is  anterior  and  mesial  to 
Gowers's,  encroaching  some  upon  the  anterior  region 
of  the  cord.     The  fibers  of  this  tract  are  supposed  to 
come  from  cells  in  Deiters'  nucleus  of  the  medulla 
which  may  be  regarded  as  an  internode  between  the 
cerebellum  and  the  medulla.     This  tract  descends 
as  far  as  the  lumbar  region  and  its  fibers  are  supposed 
to  arborize  around  the  motor  cells  of  the  anterior 
horn  of  the  spinal  cord. 

5.  The   mixed   lateral    bundle  represents   the   re- 
mainder of  the  lateral  region.     Its  fibers  probably 
come  from  cells  in  all  parts  of  the  gray  matter  of  the 
cord,  and  from  cells  on  the  opposite  side  of  the  cord. 
At  intervals  these  fibers  ultimately  reenter  the  gray 
matter  and  arborize  about  nerve  cells.     It  is  there- 
fore an  intersegmental  or  commissural  tract,  both 
sensory  and  motor. 


THE  SPINE.  383 

ANTERIOR  REGION. 

1.  Direct  Pyramidal  Tract. — This  is  a  small  well- 
defined  tract  that  lies  next  to  the  antero-median 
fissure.     As  a  rule  this  tract  can  only  be  traced  down 
to  the  middle  of  the  dorsal  region.     These  fibers 
originate  jointly  with  those  of  the  crossed  pyramidal 
tract;   that  is,  from  the  large  pyramidal  cells  of  the 
cerebral  cortex.     The  fibers,  however,  do  not  cross 
in  the  medulla  but  pass  directly  down  the  cord  on 
the  same  side.    The  fibers  cross  in  the  cord  at  inter- 
vals in  its  course,  making  use  of  the  anterior  com- 
missure to  reach  the  opposite  side,  where  they  ar- 
borize around  the  cells  of  the  anterior  horn  in  a 
manner  like  those   of  the  crossed  pyramidal.     It 
thus  follows  that  the  motor  cells  on  one  side  of  the 
cerebrum  control  the  muscular  contraction  on  the 
opposite  side  of  the  body,  either  through  the  crossed 
or  the  direct  pyramidal  tract  or  through  both. 

2.  The  anterior  ground  bundle  is  really  a  part  of 
the  mixed  lateral  tract  already   described.     It   is 
composed  of  ascending  and  descending  fibers  that 
have  both  their  origin  and  their  termination  in  the 
gray  matter  of  the  cord  and  is  therefore  an  inter- 
segment al  or  commissural  tract. 

3.  Anterior  White  Commissure. — This  is  composed 
of  medullated  nerve  fibers  passing  parallel  to  the 
gray  commissure  between  the  latter  and  the  bottom 
of  the  anterior  fissure.     It  is  a  decussation  of  fibers 
of  a  mixed  variety,  many  of  them  being  derived 
from  the  direct  pyramidal  tract  as  already  stated. 


CHAPTER  XIII. 
THE  BRAIN. 

The  brain,  or  encephalon,  develops  jointly  will 
the  spinal  cord,  and  represents  the  anterior  extremit} 
of  the  cerebrospinal  axis.  The  average  weight  of 
the  brain  is  about  forty-eight  ounces,  while  the  cord 
weighs  less  than  one  ounce.  Like  the  cord  it  is  an 
organ  in  which  all  the  elementary  tissues  may  be 
found  but  in  which  the  neurons  predominate. 
During  embryonic  growth  the  brain  and  cord  are  a 
hollow  tube  and  this  cavity  is  never  obliterated,  but 
remains  in  the  brain  as  its  ventricles.  Develop- 
mental history  further  discloses  the  fact  that  the 
brain,  like  the  cord,  is  made  up  of  definite  segments 
or  joints  called  neuromeres.  These  primary  units 
are  soon  replaced  by  three  larger  vesicles  called 
primary  fore-brain,  mid-brain,  and  hind-brain.  It 
is  generally  affirmed  that  the  first  of  these  repre- 
sents 3  neuromeres,  the  second  2  neuromeres,  and 
the  third  6  neuromeres.  Later  the  primary  fore- 
brain  divides  to  form  the  cerebrum  and  the  'tween- 
brain,  while  the  hind-brain  also  divides  to  form  the 
cerebellum  and  medulla.  In  the  adult  brain,  there- 
fore,  five  divisions  may  be  recognized,  each  of  them 
presenting  a  central  canal  or  cavity  as  designated  in 
the  table  below : 

384. 


THE   BRAIN.  385 

Primary  Divisions.             Secondary  Divisions.  Cavity. 

Fore-brain   or   prosen-    f  T"  Jelencephalon  or  cerebrum.  Lateral  ventricle. 

cenhalon                         1  2'   *  halamencephalon,  or  dien-  Third  ventricle. 

'     (  cephalon,  or  'tween-brain. 

Mid-brain.                              3.  Mesencephalon  or  mid-brain.  Aqueduct  of  Sylvius. 

Hind-brain   or  rhomb-    f  4>  Metencephalon    or     cerebel-  Upper  part  of  fourth 

pnrenhalnn                                              mm.  ventricle. 

'     (  5.  Myelencephalon  or  medulla.  Fourth  ventricle. 


The  brain  is  thus  a  hollow  multiple  organ.  Its 
central  cavity  is  lined  with  a  serous  membrane,  the 
ependyma,  which  secretes  a  serous  fluid,  the  cerebro- 
spinal  fluid.  The  outer  vascular  investments  are  the 
meninges,  which  serve  as  a  delicate  packing  between 
the  brain  wall  and  the  bony  vault  of  the  cranium. 

The  Meninges.  —  These  are  three  connective-tissue 
investments  to  the  brain  that  are  practically  identical 
and  continuous  with  those  already  described  inclos- 
ing the  cord.  It  will  be  sufficient,  therefore,  to  men- 
tion the  points  wherein  these  membranes  slightly 
differ. 

The  dura  of  the  brain  forms  the  periosteum  of  the 
investing  bones,  while  each  segment  of  the  vertebral 
column  has  its  own  periosteum.  Several  broad 
prolongations  of  the  brain  dura  extend  between  the 
different  divisions  of  the  brain.  These  are  the  ten- 
torium  between  the  cerebrum  and  the  cerebellum; 
the  falx  cerebri  which  dips  into  the  great  fissure  be- 
tween the  two  lobes  of  the  cerebrum,  and  the  falx 
cerebelli,  which  is  a  small  median  septum  between 
the  cerebellar  hemispheres.  At  the  basal  skull  fora- 
mina, the  dura  accompanies  the  cranial  nerves  and 
is  continuous  with  the  areolar  sheaths  of  these 
nerves. 

The  pia  is  composed  mostly  of  areolar  tissue  and 


386     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

small  blood-vessels.  It  is  the  nourishing  tissue  of 
the  brain  and  clothes  its  entire  surface,  dipping 
down  to  the  bottom  of  fissures,  and  sending  strands, 
associated  with  blood-vessels,  into  the  brain  sub- 
stance. The  brain  pia  is  more  vascular  than  that  of 
the  cord. 

The  arachnoid  is  a  wTeb-like  membrane  between  the 
dura  and  the  pia,  but  much  nearer  the  dura.  The 
space  beneath  the  dura  is  called  the  subdural  space, 
and  is  small.  That  between  the  arachnoid  and  pia 
is  larger  and  is  called  the  subarachnoid  space.  The 
former  has  a  little  serous  fluid,  and  the  latter  is  filled 
with  lymph  and  some  cerebrospinal  fluid.  This 
fluid  reaches  the  external  surface  of  the  brain  through 
a  small  foramen  or  pore  in  the  thin  roof  of  the  fourth 
ventricle.  Trabeculae  intervene  between  all  these 
membranes. 

THE  MEDULLA. 

The  medulla  is  about  one  inch  in  length,  and  rep- 
resents the  portion  of  the  brain  next  to  the  spinal 
cord.  Its  lower  extremity  is  at  the  lower  margin  of 
the  foramen  magnum.  From  this  point  it  passes 
upward  in  nearly  a  vertical  direction  to  its  upper  ex- 
tremity at  the  lower  border  of  the  pons.  Being  the 
nerve  center  for  the  large  cranial  nerves,  the  medulla 
is  the  most  vital  part  of  the  brain,  and  the  best  pro- 
tected. Its  lower  portion  resembles  the  cord,  having 
the  same  fissures  and  grooves.  The  upper  portion  is 
expanded  in  such  a  manner  as  to  bring  its  cavity  or 
fourth  ventricle  to  the  dorsal  surface.  This  ex- 
panding process  has  carried  the  dorsal  tracts  later- 


THE   BRAIN. 


387 


ally,  leaving  a  very  thin  roof,  consisting  of  the 
ependyma  and  a  vascular  pia,  to  cover  the  ventricle. 
The  lower  half  of  the  fourth  ventricle  is  found  in  the 
upper  half  of  the  medulla,  while  the  upper  half  of 
this  ventricle  extends  into  the  pons  region  and  is 
overlaid  by  the  cerebellum.  The  central  canal  of 
the  cord  opens  into  the  lowest  point  of  this  ventricle 
and  therefore  extends  through  the  lower  half  of  the 
medulla,  but  nearer  its  dorsal  surface.  The  lower 


Valve'  of  Vieussens. 

Middle  peduncle  of  the 
cerebellum. 

Area  acustica. 

Trigonum  vagi. 

Calamus  scriptorcs. 


Pineal  body. 

Superior  quadrigeminal  body. 
Inferior  quadrigeminal  body. 

Crus  cerebri. 

Superior  peduncle  of  the 

cerebellum. 
Eminentia  teres. 

Stria,  acustica. 
Restiform  body. 
Trigonum  hypoglossi. 

Clava. 

Rolandic  tubercle. 

Funiculus  gracilis. 
Funiculus  cuneatus. 


Fig.  269.— Dorsal  view  of  'the  medulla,  pons  and  mid-brain. 

- 

half  is  therefore  spoken  of  as  the  closed  medulla 
while  the  upper  part,  that  has  the  ventricle,  is 
called  the  open  medulla. 

Two  ridges,  the  funiculus  gracilis  and  funiculus 
cuneatus,  may  be  recognized  on  the  dorsal  surface  of 
the  medulla,  and  represent  the  continuation  of  the 
columns  of  Goll  and  Burdach.  The  funiculus  gra- 
cilis terminates  anteriorly  in  a  blunt  expansion 


388     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


called    the    claua.      On  the 


Fig.  270. — View,  from  below,  of  the 
connection  of  the  principal  nerves 
with  the  brain:  I',  the  right  olfactory 
tract;  II,  the  left  optic  nerve;  IF,  the 
right  optic  tract  (the  left  tract  is  seen 
passing  back  into  i  and  e,  the  internal 
and  external  corpora  geniculata); 
III,  the  left  oculomotor  nerve;  IV,  the 
trochlear;  V,  V,  the  large  roots  of  the 
trifacial  nerves;  +  -}-,  the  lesser  roots 
(the  +  of  the  right  side  is  placed  on 
the  Gasserian  ganglion);  i,  the  oph- 
thalmic; 2,  the  superior  maxillary; 
and  3,  the  inferior  maxillary  divi- 
sions; VI,  the  left  abducens  nerve; 
VII,  VIII,  the  facial  and  auditory 
nerves;  IX-XI,  the  glossopharyngeal, 
pneumogastric,  and  spinal  accessory 
nerves;  XII,  the  right  hypoglossal 
'nerve;  Clt  the  left  suboccipital  or  first 
cervical  nerve  (Nancrede). 


dorsal  aspect  of  the 
open  medulla  is 
found  the  restiform 
body,  which  passes  in- 
to the  inferior  pedun- 
cle of  the  cerebellum 
and  represents  fiber 
tracts,  the  most  im- 
portant being  the  di- 
rect cerebellar  tract. 
The  lower  half  of  the 
fourth  ventricle  is  V-- 
shaped and  its  apex 
is  called  the  calamus 
scriptoriuSy  from  its 
resemblance  to  a  pen. 
In  its  floor  three  tri- 
angular areas  are 
found,  called  trigo- 
num  vagi,  trigonum 
hypoglossi,  and  area 
acusticcz.  It  is  in 
these  areas  that  we 
find,  respectively,  the 
origin  of  the  tenth, 
twelfth,  and  eighth 
cranial  nerves.  The 
stria  acusticce  are 
transverse  ridges  in 
the  floor  of  this  ventri- 
cle, extending  across 
its  middle  part  from 
the  median  sulcus  to 


THE    BRAIN.  389 

the  lateral  margins,  and  represent  nerve  fibers  car- 
rying impulses  from  the  eighth  cranial  nerve. 

On  the  lateral  surface  of  the  medulla  a  prominent 
oval  elevation  appears  called  the  olivary  body, 
which  represents  a  crescent  collection  of  nerve  cells. 
Just  dorsal  to  the  olivary  body  is  the  continuation 
of  the  dorsal  groove  of  the  cord,  and  it  is  from  this 
groove  that  fibers  of  the  ninth,  tenth,  and  eleventh 
cranial  nerves  emerge.  Near  the  anterior  extremity, 
at  the  lower  margin  of  the  pons,  is  the  superficial 
origin  of  the  seventh  and  eighth  nerves.  The  origin 
of  these  nerves  corresponds  to  the  entrance  into  the 
cord  of  the  posterior  root  of  the  spinal  nerves.  Just 
median  or  ventral  to  the  olive  is  a  groove  that  cor- 
responds to  the  points  of  exit  of  the  anterior  root  of 
the  spinal  nerves.  From  this  groove  the  fibers  of 
the  twelfth  cranial  nerve  escape. 

The  ventral  region  of  the  medulla  presents  a 
median  fissure,  the  continuation  of  the  anterior 
fissure  of  the  cord.  The  upper  end  of  this  fissure 
forms  a  pit  at  the  lower  margin  of  the  pons,  called 
the  foramen  cecum.  Just  lateral  to  this  cecum,  and 
curving  around  the  pons,  is  the  superficial  origin  of 
the  sixth  pair  of  cranial  nerves.  On  each  side  of  the 
median  fissure  is  a  longitudinal  ridge  called  the  pyr- 
amids which  represents  the  fibers  of  both  the  crossed 
and  the  direct  pyramidal  tract.  Near  the  lower  ex- 
tremity of  the  medulla  the  fissure  seems  partly 
obliterated  by  ridges  recrossing.  These  represent 
pyramidal  fibers  crossing  to  form  the  crossed  pyr- 
amidal tract,  and  constitute,  therefore,  the  motor 
decussation.  Just  below  the  olive  curved  striae  may 


390     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

be  seen,  that  appear  to  come  from  the  median  fissure 
and  sweep  around  the  olive  and  enter  the  cerebellum 
through  the  restiform  body  and  inferior  peduncle. 
These  are  called  the  superficial  arcuate  fibers,  and 
many  of  them  come  from  the  nerve  cells  of  the  olive 
of  both  the  same  and  the  opposite  sides. 

Sections   of  the   Medulla. — Cross  Sections  of  the 
Closed  Medulla. — These  verify  the  surface  markings 


Median 
raphe. 


Central  canal.  Funiculus  gracilis. 

Nucleus  gracilis. 

Funiculus  cuneatus. 

Nucleus  cuneatus. 
Spinal  root  of  fifth 

nerve. 
Sub  slant  ia  gelati- 

nosa  Rolando. 
Deep  arcuate  fibers. 

Mesial  olive. 
Decussation  of  fibers. 
Superficial  arcuate. 

Olive  nucleus. 

Arcuate  nucleus. 
Anterior  Pyramids. 

Fig.  271. — Cross  section  of  the  closed  medulla. 


already  described.  In  the  dorsal  region  is  the  funiculi 
gracilis  and  cuneatus,  fiber  tracts  of  the  columns 
of  Goll  and  Burdach.  Beneath  these  are  the  nuclei 
of  gracilis  and  cuneatus,  nerve  cells  around  which 
arborize  the  telodendria  of  the  fibers  of  the  columns 
of  Goll  and  Burdach.  From  these  nerve  cells  axones 
spring  that  sweep  downward  and  across  to  the  oppo- 
site side,  and  in  crossing  form  the  sensory  decussa* 


THE   BRAIN.  391 

lion.  It  thus  happens  that  the  sensory  impulses  also 
cross  and  reach  the  opposite  side  of  the  brain.  Ex- 
ternal to  the  nucleus  gracilis  is  the  substantia  gelati- 
nosa  of  Rolando,  a  continuation  of  that  of  the  cord. 
Just  external  to  this  is  a  cross  section  of  nerve 
fibers,  the  ascending  root  of  the  fifth  nerve.  The 
central  area  of  each  half  of  the  section  shows  a  large 
number  of  scattered  nerve  fibers  interlacing  and  in 
cross  sections.  This  area  is  called  the  formatio 
reticularis.  Anterior  to  it,  a  collection  of  nerve  cells 
represents  the  olivary  body,  median  and  dorsal  to 
which  a  second  and  smaller  collection  of  cells  consti- 
tute the  mesial  olivary  nucleus.  The  bulk  of  the 
anterior  portion  shows  a  cross  section  of  the  pyra- 
mids. Some  of  these  fibers  may  be  seen  to  sweep 
to  the  opposite  side,  thus  making  the  motor  decus- 
sation.  In  doing  so  they  seem  to  pass  over  in  large 
alternate  bundles,  rather  than  uniformly,  as  is  the 
case  with  the  sensory  decussation.  At  the  anterior 
surface  on  each  side  of  the  median  fissure  and  sweep- 
ing around  the  pyramids  are  the  superficial  arcuate 
fibers,  and  also  a  collection  of  nerve  cells,  the  arcuate 
nucleus. 

In  cross  sections  of  the  open  medulla  the  resem- 
blance to  that  of  the  cord  is  less  distinct.  The  thin 
roof  of  the  fourth  ventricle  is  usually  broken,  leaving 
a  dorsal  expanded  cleft.  The  lateral  margin  or 
remnant  of  the  roof  is  called  the  lingula.  Just  be- 
neath the  floor  and  close  to  the  median  sulcus  are 
the  nerve  cells  of  the  twelfth  nerve.  Lateral  but  in 
close  proximity  to  these  are  the  nerve  cells  of  the 
tenth  nerve.  The  axones  from  these  cells  may  be 


392     NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

traced  through  the  substance  of  the  medulla  to  their 
ventral  exit.  The  superficial  origin  of  the  twelfth 
nerve  is  just  anterior  to  the  olive,  and  the  fibers  of 
the  tenth  nerve  may  be  traced  to  their  superficial 
origin  just  dorsal  to  the  olive.  In  serial  cross  sec- 


Nucleus  am- 

'  'juus. 
Substantia 

gelatinosa 

Rolando. 
Descending  root 

of -nerve  V. 


Nucleus 
later  a  Us. 

A  nt.  lat.  ascend^ 
ing  tract. 


Olive. 


Superficial 

arcuate  fibers. 
Arcuate  nucleus* 


Anterior  pyramids. 
Fig.  272. — Cross  section  of  the  open  medulla  (composite  drawing). 

tions  it  will  be  seen  that  the  nuclei  of  the  other  cra- 
nial nerves,  from  the  sixth  to  the  twelfth,  lie  in  the 
floor  of  the  fourth  ventricle. 

The  fasciculus  solitarius  is  a  bundle  of  nerve  fibers, 
cut  in  cross  section,  and  placed  just  lateral  to  the 


THE    BRAIN/  393 

nucleus  of  the  tenth  nerve.  This  bundle  represents 
fibers  from  the  ninth  and  tenth  nerves.  Just  in- 
ternal or  mesial  to  this  bundle  are  a  few  cells  called' 
the  solitary  nucleus.  This  is  probably  a  motor  nu- 
cleus of  the  ninth  and  tenth  nerves.  Lateral  to  the 
solitary  fasciculus  are  the  fibers  of  the  large  restiform 
body  on  their  way  to  the  cerebellum. 

The  posterior  longitudinal  bundle  is  a  tract  of 
nerve  fibers  that  appears  in  cross  section  just  an- 
terior to  the  nucleus  of  the  twelfth  nerve,  and  lies  in 
close  apposition  to  the  median  plane.  The  formatio 
reticularis  occupies  the  greater  part  of  the  center  of 
each  lateral  half  of  the  medulla,  and  presents  the 
same  appeareance  as  in  sections  of  the  closed  med- 
ulla. Likewise  the  cells  of  the  olivary  body,  which 
in  the  open  medulla  form  a  large  conspicuous  nu- 
cleus that  takes  the  form  of  a  U  with  wavy  sides,  and 
with  the  open  extremity  turned  inward  and  upward. 
Nerve  fibers  from  its  hilum  sweep  across  to  the  oppo- 
site side  and  some  curve  around  to  join  the  super- 
ficial arcuate  fibers  of  the  same  side. 

The  arcuate  fibers  are  divided  into  the  deep  and 
the  superficial  set.  The  deep  set  come  from  the  nuclei 
cutieatus  and  gracilis  and  from  the  sensory  nuclei  of 
the  cranial  nerves.  From  this  source  they  arch  to 
the  opposite  side  and  then  turn  to  pass  upward  in 
the  brain  stem,  where  they  form  the  middle  fillet. 
The  superficial  set  may  be  divided  into  an  anterior 
and  a  posterior  group.  The  anterior  group  originate 
in  the  nuclei  gracilis  and  cuneatus,  accompany  the 
deep  set  to  the  opposite  side  of  the  medulla,  where 
some  of  them  become  superficial  in  the  anterior 
mesial  fissure,  then  curve  around  the  anterior  pyra- 


394     NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

mid  in  the  superficial  border  of  the  medulla,  and 
finally  enter  the  restiform  body  and  the  cerebellum 
through  the  inferior  cerebellar  peduncle.  Others 
become  superficial  in  the  antero-lateral  groove  lateral 
to  the  anterior  pyramid,  passing  also  to  the  cerebel- 
lum, through  the  inferior  cerebellar  peduncle. 

The  posterior  group  originate  in  the  nuclei  gracilis 
and  cuneatus  and  pass  directly  forward  and  up- 
ward in  the  cerebellar  peduncle  of  the  same  side  to 
terminate  in  the  cerebellum.  All  the  arcuate  fibers 
carry  sensory  impulses. 

The  arcuate  nucleus  is  a  collection  of  nerve  cells 
interposed  in  the  anterior  superficial  arcuate  fibers  at 
a  point  just  anterior  to  the  pyramids  of  the  medulla. 

SUMMARY  OF  TRACTS,  THEIR  ORIGIN  AND  TERMINA- 
TIONS. 


Columns. 

1.  Column  of  Goll  .  . 

2.  Column  of  Burdach 

3.  Comma  tract    .  .  . 

4.  Lissaur's  tract    .  . 

5.  Direct  cerebellar  . 

6.  Gowers's  tract    .  . 


7.  Lowenthal 

8.  Lateral  ground  bundle. 

9.  Crossed  pyramidal    .   . 

10.  Direct  pyramidal   .   :   . 

11.  Ant.  ground  bundle  .   . 


Origin  of  Axones. 
Cells  of  dorsal  ganglion. 
Cells  of  posterior  horn. 
Same  as  column  of  Goll. 
Dorsal  ganglion  .  .  .  . 
Dorsal  ganglion  .  .  .  . 
Cells  of  col.  of  Clarke  . 


Cells  of  post,  horn 

Deiters'  nucleus  . 

Cells  of  cord  .   .  . 

Cerebral  cortex  . 

Cerebral  cortex  . 

Cells  of  cord  .   .  . 


Terminations. 
i.  Nucleus  gracilis. 

i.  Nucleus  cuneatus. 
i.  Cells  of  post.  horn, 
i.  Cells  of  post.  horn, 
i.  Cerebellum. 

1.  Cerebellum. 

2.  Corp.  quadrigemina. 

3.  Thalamus. 

4.  Substantia  nigra. 

5.  Lenticular  nucleus, 
i.  Cells  of  ant.  horn, 
i.  Cells  of  cord. 

i.  Cells  of  ant.  horn, 
i.  Cells  of  ant.  horn. 
i.  Cells  of  cord. 


The  sensory  tracts  are  Nos.  i,  2,  3,  4,  5,  6.    The  motor  tracts  are  Nos.  7,  9,  10. 
The  mixed  tracts  are  Nos.  8,  n. 


THE  PONS. 

The  pons  represents  the  anterior  basal  portion  of 
the  hind-brain.  It  is  an  oval  body,  one  inch  long, 
one  inch  thick,  and  about  one  and  one-half  inches 
broad.  It  is  a  junctional  piece  between  the  medulla 


THE)   BRAIN. 


39S 


and  the  mid-brain  and  the  overlying  cerebellum. 
The  upper  half  of  the  fourth  ventricle  is  confined  to 
its  dorsal  aspect;  that  is,  between  the  pons  and  the 
cerebellum.  Viewed  from  the  ventral  surface  it  pre- 
sents the  appearance  of  a  rhomboid  with  striations 
that  pass  transversely  and  become  constricted  later- 
ally to  form  the  middle  peduncles  of  the  cerebellum. 


Nucleus  of  nerve  VI. 


Restiform  body. 

Arcuate  fibers. 

Descending  root  of 
nerve  V. 

Nucleus  of  nerve  VII- 

s\ 


'  •  .v\  "v    »y :  _  '-  *  ^ --v'jr>s'?S5SsS_ 


Middle  peduncle  of 
cerebellum. 


Nuclei  pontis. 


Floor  of  fourth 
ventricle. 

Posterior  longitudinal 
bundles. 

Ascending  root  of 
nerve  VII. 

Formatio  reticularis. 
Median  raphe. 


Pyramidal  bundles. 


Transverse  fibers  of  pons. 
Fig.  273. — Cross  section  through  the  lower  part  of  the  pons. 

The  fifth  cranial  nerve,  with  its  large  sensory  root 
and  its  small  motor  root,  is  attached  to  the  ventral 
aspect  of  the  pons,  nearer  its  upper  than  its  lower 
border.  The  anterior  pyramids  seem  to  enter  the 
pons  from  below,  and  emerge  above  the  pons,  where 
they  become  lost  in  the  crura  cerebri. 

In  a  transverse  section  the  pons  presents  the  fol- 
lowing parts: 


396     NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

I.  White  matter. 

1.  Transverse    fibers — (a)    superficial,    (ft) 
deep  (trapezium). 

2.  Longitudinal  fibers — (a)  superficial  (an- 

terior pyramids),  (fe)  deep. 

3.  Posterior  longitudinal  bundle. 

4.  Fibers  of  fifth,  sixth,  seventh,  and  eighth 

cranial  nerves. 

5.  Formatio  reticularis. 

6.  Median  raphe. 

7.  Fillet — mesial  and  lateral. 

II.  Gray  matter. 

1.  Nucleus  pontis. 

2.  Superior  olive. 

3.  Nuclei  the  origin  of  fifth,  sixth,  seventh, 

and  eighth  cranial  nerves. 

Transverse  Fibers. — The  superficial  and  the  deep- 
set  of  transverse  fibers  of  the  pons  pass  into  the  cere- 
bellum through  the  middle  peduncle.  Some  of  the 
fibers  are  commissural  between  the  two  halves  of  the 
cerebellum,  while  others  connect  with  the  nuclei 
pontis  on  the  same  side  or  the  opposite  side.  In  the 
lower  portion  of  the  pons,  near  the  medulla,  the  deep- 
set  are  called  the  trapezium,  on  account  of  their 
trapezoid  arrangement. 

Longitudinal  Fibers. — The  superficial  set  repre- 
sents mostly  longitudinal  bundles  of  the  anterior 
pyramids  that  interlace  the  transverse  fibers.  The 
deep-set  are  near  the  dorsal  aspect  of  the  pons  and 
comprise  at  least  three  groups:  (i)  the  posterior 
longitudinal  bundle  near  the  median  raphe  in  which 


THE    BRAIN. 


397 


are  found  fibers  from  the  antero-lateral  column  of  the 
cord;  (2)  the  lemniscus  or  fillet,  a  continuation  of  the 
sensory  decussation;  (3)  the  fasciculus  teres,  just 
dorsal  to  the  posterior  longitudinal  bundle,  and 
which  contain  fibers  of  the  seventh  cranial  nerve. 

Fibers  of  the 
cranial  nerves  pass 
through  the  medulla 
from  their  nuclei  in 
the  dorsal  portion 
to  their  various  su- 
perficial exits  on  the 
ventral  surface. 

The  formatio  re- 
ticularis  is  similar 
to  that  described  in 
the  medulla.  The 
median  raphe  is  also 
a  continuation  of 
that  described  in 
the  medulla. 

Gray  Matter  of  the 
Pons .  —  The  nuclei 
pontis  are  nerve  cells 
that  are  scattered 
among  the  superficial  transverse  fibers  and  are  nodal 
points  forming  connections  between  the  medulla, 
cerebellum,  and  higher  brain  centers.  The  superior 
olive  lies  in  the  formatio  reticularis  and  is  seen  only 
in  the  lower  portions  of  the  pons.  The  nuclei  of  the 
cranial  nerves  are  found  in  the  dorsal  aspect,  most 
of  them  just  beneath  the  floor  of  the  fourth  ventricle. 


Nerve- 
fiber 
layer. 

Fig.  274. — Section  through  the  hu- 
man cerebellar  cortex  vertical  to  the  sur- 
face of  the  convolution.  Treatment  with 
Muller's  fluid  (Bohm  and  Davidoff). 


398        NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

THE  CEREBELLUM. 

The  cerebellum  is  next  in  size  to  the  cerebrum  and 
overlies  the  fourth  ventricle.  It  is  characterized  by 
transverse  curved  sulci  which  divide  it  into  lamellae, 
giving  the  organ  a  foliate  appearance.  A  cross  sec- 
tion of  the  lamellae  shows  a  central  core  of  white 
matter  with  a  gray  cortex,  giving  the  section  the 
appearance  of  a  branching  tree,  hence  the  name  arbor 
mtcz.  A  section  taken  in  this  plane  presents  the 
following  layers : 

1.  Molecular  layer — on  the  outside. 

(1)  Small  cortical  cells. 

(2)  Stellate  cells. 

(3)  Cells  of  Purkinje. 

2.  Granular  layer. 

1 i )  Granular  cells . 

(2)  Large  stellate  cells. 

3.  Medullary  substance — core  of  nerve  fibers. 

(1)  Centrifugal  neuraxes  from  Purkinje  cells. 

(2)  Centripetal  neuraxes. 

(a)  Mossy  fibers. 

(b)  Climbing  fibers. 

(3)  A  few  ganglion  cells  forming  the  central 

gray  nucleus. 

Molecular  Layer. — The  small  cortical  cells  are 
found  in  all  parts  of  this  layer,  but  more  especially 
near  its  periphery.  They  are  multipolar  cells  and 
but  little  is  known  of  the  distribution  of  their  neu- 
raxes. The  stellate  cells  are  evenly  distributed,  and  of 
particular  interest  are  their  neuraxes.  The  latter  pos- 
sess two  types  of  collaterals.  One  set  forms  branches 
among  the  cortical  cells,  while  a  second  class  branches 


Stellate 
cell. 


Neuraxis 
Large    of  cell  of 

stellate   granular    Tolodendrion  of  collateral 
cell.        layer,  of  climbing  fiber. 


K 

<u.§ 

ail 

A 

73  O 
.•£  <-> 
g  <u 

J/S 

W)"§J 

C   p 

3  2 
S3 

w  c 
^  o 

GJ  73 
(U  u 

^s 

c"3 

I! 


^o- 


iffl  HP 

•a      s  S       O    r< 

a  «     u  •? 


K««  > 


I 


h  *1§ 

<3     I  «B 


ce/i.         Molecular  layer 


Granular  layer.       Medullary  layer 


400     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

at  a  level  with  the  Purkinje  cells,  where  it  forms  a 
basket-like  net  around  the  bodies  of  these  cells.  The 
cells  of  Purkinje  are  the  largest  nerve  cells  in  the  body 
(about  6o//  in  diameter  or  seven  times  the  diameter 
of  a  red  blood-corpuscle).  They  form  a  single  row 
of  cells,  placed  with  considerable  regularity  some 
distance  apart,  along  the  inner  margin  of  the  molec- 
ular layer.  Their  neuraxes  arise  from  the  basal 
end  of  the  cell  body  and  extend  through  the  granular 
layer  and  enter  the  medulla  as  the  centripetal  fibers. 
The  other  extremity  of  the  cell  body  passes  into  one 
or  more  prominent  dendrites  that  arise  toward  the 


Neuraxis. 

Fig.  276. — Cell  of  Purkinje  from  the  human  cerebellar  cortex.     Chrome- 
silver  method  (Bohm  and  Davidoff). 

periphery  of  the  cerebellum.  These  dendrites 
branch  freely  in  one  plane,  like  an  ivy  growing 
against  the  wall,  and  this  plane  is  always  at  right 


BRAIN. 


401 


Neuraxis. 


angles  to  the  lamellae  of  the  cerebellum,  and  therefore 
sections  of  the  cerebellum  should  be  made  in  this 
plane. 

Granular  Layer. — This  layer  is  densely  packed 
with  nerve  cells  of  two  varieties.  The  granular 
cells  are  most  numerous,  small,  and  have  only  a  few 
dendrites  that  end  in  hook-like  telodendria.  The 
neuraxes  from  these  cells  pass  vertically  into  the 
molecular  layer,  where  many  of  them  form  a  T-- 
shaped division,  the  two  end  branches  passing  par- 
allel with  the  laminae  and  therefore  into  a  plane 
vertical  to  that  of  the  den- 
drites of  the  Purkinje  cells. 
Large  stellate  cells  form  the 
second  variety  of  this  layer. 
They  are  few  in  number 
and  lie  close  to  the  mo- 
lecular. Their  dendrites 
branch  in  all  directions  and 
their  neuraxes  form  telo- 
dendria among  the  granu- 
lar cells. 

The  medullary  substance 
may  be  divided  into  centri- 
petal fibers, — those  that 
carry  nerve  impulses  toward 
the  granular  and  molecular 
layers,  and  centrifugal  fibers; 
those  that  carry  impulses  in  the  opposite  direction. 
The  latter  are  the  neuraxes  of  the  cells  of  Purkinje, 
The  centripetal  fibers  are  the  mossy  fibers,  that  form 
mossy  telodendria  in  the  granular  layer,  and  also  so- 
called  climbing  fibers  that  pass  through  the  granular 


Claw-like  telodfn- 
drion  of  dendrite. 


Fig.  277. — Granular  cell 
from  the  granular  layer  of 
the  human  cerebellar  cortex. 
Chrome-silver  method  (Bohm 
andDavidoff). 


Layer  of    polym- 
orphous cells. 


Fig.  278. — Portions  of  vertical  section  of  human  cerebral  cortex, 
treated  by  the  Golgi  method.  The  figure  shows  the  arrangement  of  the 
different  cells  of  the  cerebral  cortex  (Sobotta). 

402 


Layer  of  small 
Pyramidal  cells. 


Layer  of  large 
pyramidal  cells. 


THE    BRAIN.  403 

layer  and  connect  with  the  dendrites  of  Purkinje 
cells,  up  which  they  seem  to  climb.  Collaterals  are 
given  off  in  their  passage  through  the  granular  layer. 
The  central  gray  nucleus  forms  the  central  core  of 
each  lateral  cerebellar  hemisphere.  It  forms  a  cap- 
sule of  gray  matter  from  whose  hilum  many  nerve 
fibers  pass,  the  majority  to  enter  the  superior  cerebel- 
lar peduncle. 

THE  CEREBRAL  CORTEX. 

The  cerebrum  is  such  an  extensive  and  complicated 
organ  that  only  a  description  of  the  cortex  in  the 
region  of  the  fissure  of  Rolando  will  be  given  here. 
From  without  inward  this  region  presents,  rather 
indistinctly,  the  following  layers:  (T)  molecular 
layer;  (2)  small  pyramidal  cells;  (3)  large  pyr- 
amidal cells;  (4)  polymorphic  cells;  (5)  medullary 
substance  of  nerve  fibers.  '  It  is  to  be  borne  in  mind 
that  this  cortex  presents  many  fissures  and  minor 
folds  into  which  the  pia  dips,  and  that  a  transverse 
section  is  any  plane  that  is  vertical  to  the  folded 
surface. 

i.,  The  molecular  or  outer  layer  is  composed  chiefly 
of  nerve  fibers  which  interlace  in  all  directions  but 
which  have  chiefly  a  direction  parallel  to  the  external 
surface.  The  chief  dendrite  of  the  pyramidal  cells 
terminates  in  this  layer  in  tuft-like  telodendria,  and 
also  ascending  neuraxes,  mostly  from  the  polymor- 
phous cells.  The  cells  of  this  layer  are  few,  and  have 
been  described  as  polygonal,  spindle-shaped,  and 
triangular,  or  stellate.  Their  neurons  are  nearly  all 
confined  to  this  layer,  the  axones  of  only  a  few  reach 
down  to  the  deeper  layers. 


404    NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

2.  The  layer  of  small  pyramidal  cells  is  not  well 
defined  and  usually  not  so  broad  as  the  molecular 
layer.  The  nerve  cells  have  a  triangular  body,  the 
apex  being  directed  toward  the  surface  of  the  cortex. 
From  this  apex  a  primordial  dendrite  ascends  and 


Brush-like  telodendrion. 


Main  dendrite. 


Secondary  dendrite. 


Basal  dendrite.' 


Neuraxis  with  collaterals-—— 


Fig.    279. — Large   pyramidal  cells  from   the  human   cerebral  cortex, 
Chrome-silver  method  (Bohm  and  Davidoff). 

gives  off  a  number  of  branches  that  end  in  terminal 
filaments  or  telodendria  in  the  outer  layer,  frequently 
at  the  brain  surface.  Several  short  dendrites  arise 


THE   BRAIN. 


405 


~  d 


from  the  basal  surface  of  the  cell  body  where  also 
the  axone  is  attached.  The  latter  passes  toward 
the  medullary 
substance,  and 
near  the  cell 
body  is  pro- 
vided with  col- 
laterals that 
connect  with 
adjacent  neu- 
rons. 

The  layer  of 
large  pyramidal 
cells  comprises 
a  broad  area. 
The  cells  meas- 
ure 20  p.  to  30  fJt 
in  diameter,  be- 
ing twice  as 
large  as  those 
of  the  preced- 
ing layer.  In 
all  other  re- 
spects the  cells 
of  this  layer  re- 
semble  the 
small  pyram- 
idal cells. 
Their  dendrites 

and  axones  also  occupy  the  same  relation  as  those 
of  the  preceding  layer. 

4.  The  layer  of  polymorphic  cells  usually  includes 


if--/ 


Fig.  280.— Schematic  diagram  of  the  cerebral 
cortex:  a,  Molecular  layer  with  superficial  (tan- 
gential) fibers;  b,  striation  of  Bechtereff-Kaes; 
c,  layer  of  small  pyramidal  cells;  dt  stripe  of 
Baillarger;  e,  radial  bundles  of  the  medullary 
substance;  /,  layer  of  polymorphous  cells 
(Bohm  and  Davidoff). 


406      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

a  few  large  pyramidal  cells,  and  it  is  not  well  defined 
from  the  preceding  layer.  There  is  present  in  this 
layer:  (i)  multipolar  cells  with  short  neuraxes  (Golgi 
cells)  whose  dendrites  project  in  all  directions ;  and 
(2)  cells  with  slightly  branched  dendrites  and  with 
neuraxes  passing  toward  the  surface  of  the  brain 
where  they  terminate  in  the  molecular  outer  layer. 
The  cells  of  this  layer  are  triangular  or  spindle-shaped 
and  vary  considerably  in  size. 

5.  The  medullary  substance  is  composed  of  a  mass 
of  nerve  fibers  that  take  a  radial  course  and  in  which 
we  can  detect  no  structural  difference.  Physio- 
logically, however,  we  can  divide  them  into  four 
classes  as  follows :  i ,  projecting  or  centrifugal  fibers 
which  indirectly  connect  the  cerebral  elements  with 
the  periphery  of  the  body;  that  is,  they  carry  im- 
pulses away  from  the  nerve  center;  2,  commissural 
fibers  that  connect  corresponding  parts  of  the  two 
cerebral  hemispheres  through  the  corpus  callosum; 
3,  association  fibers  that  connect  different  parts  of 
the  same  hemisphere ;  4,  centripetal  fibers  or  terminal 
fibers, — those  that  come  from  cell  bodies  in  the  same 
or  the  opposite  hemisphere,  or  in  some  more  distant 
nerve  center,  and  that  ultimately  arborize  about 
nerve  elements  in  the  cerebral  cortex.  In  a  strict 
sense  the  second  and  the  third  class  fall  under  either 
the  centrifugal  or  the  centripetal  group. 

THE  NEUROGLIA. 

The  neuroglia  tissue  represents  a  special  form  of 
supporting  elements  found  exclusively  in  the  central 
nervous  system  and  in  the  retina.  It  develops  from 


THE    BRAIN. 


407 


the  ectoderm  while  all  other  supporting  tissues  are 
derived  from  the  mesoderm.  The  development  of 
neuroglia  cells  is  closely  associated  with  the  origin  of 
neurons,  as  both  are  derived  from  epithelial  cells  that 
lie  primarily  near  the  central  canal  of  the  nervous 
system.  The  embryonic  neuroglia  cells  are  called 
spongioblasts,  while  those  that  develop  into  true 
nerve  elements  are 
called  neuroblasts. 
Both  kinds  pass  out 
very  early  and  per- 
manently lodge  in 
the  gray  matter. 

The  neuroglia  ele- 
ments appear  as 
cells  with  many  ra- 
diating, slender  pro- 
cesses that  are  usu- 
ally unbranched, 
and  because  of 
their  peculiar  ap- 
pearance have  been 
called  spider  cells  or 
mossy  cells,  or  astro- 
cytes.  The  cell 
bodies  contain  but 

very  little  protoplasm,  and  their  shape  is  modi- 
fied according  to  their  surroundings,  being  triangu- 
lar, or  quadrangular,  or  polyangular,  the  protoplas- 
mic processes  arising  from  their  angles.  According 
to  the  length  of  their  processes  attempts  have  been 
made  to  classify  them  as  short-rayed  astrocytes,  pos- 


Fig.  281. — Neurogliar  cells:  a,  from 
spinal  cord  of  embryo  cat;  b,  from  brain 
of  adult  cat;  stained  in  chrome-silver 
(Huber). 


408      NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

sessing  a  few  short  processes,  and  long-rayed  astro- 
cytes,  having  many  long,  slender  processes.  The 
former  appear  among  the  nerve  cells  only,  the  latter 
are  found  both  in  the  gray  and  the  white  matter. 


Fig.  282. — Typical  neuroglia  cells,  from  cross  section  of  the  white  mat- 
ter of  the  human  spinal  cord,  stained  after  Benda's  selective  neuroglia 
tissue  staining  method  (Huber,  "Studies  on  Neuroglia  Tissue," 
Vaughan  Festschrift,  1903). 


Not  infrequently  detached  processes  may  be  found 
and  processes  that  can  be  traced  directly  through 
the  bodies  of  adjacent  astrocytes.  The  neuroglia 
thus  forms  a  delicate  web-like  fabric  that  interlaces 


THE   BRAIN.  409 

the  whole  central  nervous  system,  to  which  it  gives 
substance  and  support.  It  is  to  be  remembered  that 
supporting  tissue  of  mesodermic  origin  does  the  same 
thing,  especially  in  the  cord.  The  connective-tissue 
elements  usually  accompany  the  nutrient  blood- 
vessels. 

BLOOD-VESSELS  OF  THE  CENTRAL  NERVOUS  SYSTEM, 

The  spinal  cord  receives  its  blood  supply  from  a 
plexus  of  blood-vessels  in  the  pia  mater.  There  is  an 
anterior  median  artery  just  in  front  of  the  anterior 
fissure.  Some  two  hundred  branches  from  this 
vessel  pass  at  right  angles  directly  into  the  fissure 
and  enter  the  gray  matter,  where  each  divides  into 
a  right  and  left  branch  that  enclose  the  central 
canal.  Each  arterial  branch  ultimately  bifurcates, 
just  in  front  and  external  to  the  cell  column  of 
Clarke,  forming  minute  ascending  and  descending 
terminals,  which  become  lost  in  an  extensive  capil- 
lary system  of  the  central  gray  matter.  The  white 
matter  receives  its  blood  supply  from  a  plexus  of 
vessels  situated  on  the  dorsal  and  lateral  surfaces  of 
the-  cord.  From  this  system  small  branches  enter 
the  cord  anywhere  and  form  capillaries  among  the 
nerve  fibres;  that  is,  supplies  blood  to  the  white 
matter.  The  gray  matter  has  a  more  liberal  blood 
supply  than  the  white  matter. 

The  brain  substance  also  receives  its  blood  supply 
from  a  plexus  of  blood-vessels  in  its  pia.  The  capil- 
laries are  particularly  numerous  and  closely  meshed 
wherever  the  nerve  cells  are  segregated,  that  is, 
in  the  ganglion  centers.  In  the  cerebellum  the  gran- 


410      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

ular  layer  is  the  most  vascular.  The  arterioles  have 
thin  walls,  and  in  old  age  may  become  brittle  and 
may  easily  rupture. 

No  lymphatic  vessels  with  definite  walls  have  been 
discovered  in  the  central  nervous  system.  The 
blood-vessels  are,  however,  surrounded  by  peri- 
vascular  spaces  which  probably  function  as  lymph 
channels. 


CHAPTER  XIV. 
THE  EYE. 

The  eyes  begin  to  develop  during  the  fourth  week 
of  embryonic  life,  and  appear  then  as  a  pair  of  lateral 
e vagina tions  of  the  fore-brain.  A  pair  of  vesicles 
are  thus  formed  called  the  primary  optic  vesicles. 
When  the  latter  reach  the  ectoderm  an  invagination 
of  these  vesicles  takes  place,  like  pushing  in  one 
side  of  a  hollow  rubber  ball.  The  cavity  of  the 
primary  optic  vesicle  becomes  obliterated  by  this 
process,  and  a  new  vesicle  forms,  called  the  secondary 
optic  vesicle.  It  will  be  observed  that  the  cavity  of 
this  vesicle  is  practically  the  same  as  would  be  pro- 
duced by  an  invagination  of  the  brain  wall.  Later 
it  will  be  seen  that  this  cavity  corresponds  to  the 
space  occupied  by  the  vitreous  humor  of  the  adult 
eye,  while  its  wall  becomes  the  retina.  The  stalk 
that  connects  this  vesicle  to  the  brain  is  the  optic 
stalk,  in  which  later  optic  nerve  fibers  appear. 

At  the  time  the  secondary  optic  vesicle  is  forming 
there  is  a  disc-like  thickening  of  the  adjacent  ecto- 
derm, which  soon  invaginates  and  becomes  con- 
stricted as  an  ectodermal  vesicle.  This  is  the  lens, 
which  later  takes  a  position  at  the  mouth  of  the 
secondary  optic  vesicle.  The  latter  presents,  at  this 
stage,  a  fissure  in  its  ventral  surface  called  the  cho- 
roid  fissure.  Connective-tissue  cells  migrate  through 


412      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

this  fissure  and  fill  the  cavity  of  the  secondary  vesicle. 


Fig.  283. — Part  of  a  section  through  the  head  of  an  early  human 
embryo,  showing  the  connection  of  the  primary  optic  vesicles  with  the 
fore-brain  (His):  olf,  Olfactory  area  of  epiblast;  ch.,  part  of  fore-brain 
which  gives  rise  to  cerebral  hemispheres;  th,  thalamencephalon;  p.o.v., 
primary  optic  vesicles. 


Fig.  284. — Three  successive  stages  of  development  of  the  eye,  showing 
formation  of  secondary  optic  cup  and  crystalline  lens  in  human  embryos 
of  4  mm.  (A),  6  mm.  (#),  and  8  mm.  (C)  (Tourneux):  a,  a,  primitive 
optic  vesicles;  b,  external  layer  of  secondary  optic  cup  (future  pigment 
layer  of  retina) ;  c,  inner  layer  of  cup  (retina  proper) ;  d,  lens  pit  (thick- 
ened and  depressed  ectoderm) ;  e,  lens  vesicle. 

These  cells  form  the  vitreous  humor,  while  the  choroid 


THE  EYE.  413 

fissure  closes  and  permanently  disappears.  The  ex- 
ternal coats  of  the  eye — that  is,  the  sclera  and  the 
choroid — develop  from  the  surrounding  connective 
tissue. 


Fig.  285. — Plastic  representation  of  the  optic  cup  with  lens  and  vitre- 
ous body  (Hertwig):  ab,  Outer  wall  of  the  cup;  ib,  its  inner  wall;  h, 
cavity  between  the  two  walls,  which  later  disappears  entirely;  Sn,  fun- 
dament of  the  optic  nerve  (stalk  of  the  optic  vesicle  with  a  furrow  on 
its  lower  surface);  aus,  optic  (choroid)  fissure;  glt  vitreous  body;  /,  lens. 

The  parts  of  the  adult  eyeball  may  be  tabulated  as 
follows : 

I.  Tunica  externa. 

1.  Sclera. 

2.  Cornea. 
.  II.  Tunica  media. 

1.  Choroid  coat. 

2.  Ciliary  body. 

3.  Iris. 
III.  Tunica  Interna. 

1.  Retina. 

2.  Pigment  membrane. 

The  refracting  media,  or  transparent  media  of  the 
eye  traversed  by  a  ray  of  light,  are: 
i.  The  cornea. 


414      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


2.  Aqueous  humor. 

3.  Lens. 

4.  Vitreous  humor. 

TUNICA  EXTERNA. 

i .  The  sclera  is  a  dense  connective-tissue  covering 
of  the  eye  that  terminates  anteriorly  in  the  cornea. 
It  is  of  interest  to  note  that,  in  birds  of  prey,  horny 
plates  develop  in  the  sclera  for  the  better  protection 


Canal  of  Schlemm. 


Iris. 


Cornea. 


Aqueous 
humor. 


Lash. 


Iris. 


Tunica  exierna. 


Blind 
spot. 

Optic 

nerve. 


Ciliary  body.  Ora  serrata. 

Fig.  286. — Diagram  of  the  eye. 

of  the  eye.  Posteriorly  the  sclera  is  perforated  by 
the  entrance  of  the  optic  nerve.  Connective-tissue 
fibers,  known  as  the  lamina  cribrosa,  pass  across  this 
point  and  interlace  the  optic  fibers,  while  others 
sweep  backward  along  the  optic  nerve  as  its  external 
envelope. 

The  sclera  consists  of  interlacing  bundles  of  con< 


THE  EYE. 


415 


nective-tissue  fibers  closely  felted  together.  The 
tendons  of  the  ocular  muscles  are  continuous  with 
the  scleral  fibers.  The  external  scleral  surface  is 
clothed  with  a  layer  of  flattened  endothelial  cells 
which  belong  to  the  capsule  of  Tenon.  The  latter  is 
a  loose  connective-tissue  fabric  that  invests  the  eye- 
ball, and  is  so  intimately  connected  with  the  eye 
muscles  that  coordinate 
movement  of  the  arti- 
ficial eye,  or  glass  shell, 
is  made  possible  after 
the  enucleation  of  an 
eye.  Pigmentation  is 
regularly  present  at  the 
corneal  margin  and  the 
surface  next  to  the 
choroid.  This  inner 
pigmented  scleral  sur- 
face is  lined  by  a  layer 
of  flattened  endothelial 
cells,  forming  a  sepa- 
rate membrane  and 
called  by  some  the  lam- 
ina fusca;  generally,  Fig.  287. — Section  of  the  cornea  of  the 

however,  it  is  regarded 
as  the  outermost  layer 

of  the  choroid  and  known  as  the  lamina  choroidea. 
2.  The  Cornea.— The  cornea  is  inserted  into  the 
sclerocorneal  junction  in  which  is  found  an  annular 
venous  sinus,  the  canal  of  Schlemm,  which  may  ap- 
pear as  a  single  canal  or  as  several  canals.  The 
cornea  is  a  perfectly  transparent  medium  and  free 


Substantia 
Propria. 


41 6      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY, 

from  red  blood  corpuscles,  the  nearest  blood  supply 
being  that  of  the  sclerocorneal  margin  in  the  region 
of  the  canal  of  Schlemm. 

Histologically  the  cornea  is  made  up  of  five  layers : 
i,  the  anterior  epithelium;  2,  the  anterior  elastic 
membrane,  or  Bowman's  membrane;  3,  the  ground 
substance,  or  substantia  propria;  4,  Descemet's 
membrane;  5,  the  endothelium  of  Descemet's 
membrane. 

The  corneal  epithelium  is  of  the  stratified  squamous 
variety,  a  little  thicker  near  the  corneal  margin  than 
at  its  center  and  in  the  human  eye  is  composed  of  five 
layers  of  cells.  It  is  related  to  the  epidermis  of  the 
skin,  the  cells  being  provided  with  short  prickles 
that  are  very  difficult  to  demonstrate.  This  epithe- 
lium forms  an  efficient  and  important  protection  to 
the  front  of  the  eye.  The  anterior  elastic  membrane 
measures  8  p  in  thickness,  about  the  width  of  a  red 
blood  corpuscle,  and  becomes  thinner  towards  the 
sclerocorneal  junction.  It  is  a  compact  layer  of  con- 
nective-tissue fibrils  and  is  regarded  by  some  as  a 
basement  membrane  to  the  overlying  epithelium. 
Nerve  fibers  penetrate  this  membrane  to  connect 
with  the  corneal  epithelial  cells.  The  substantia 
propria  constitutes  the  bulk  of  the  cornea.  It  con- 
sists of  bundles  and  lamellae  of  connective-tissue 
fibrils,  and  peculiarly  flattened  cells  called  corneal 
corpuscles.  The  fibrils  of  each  lamella  are  cemented 
together  and  run  parallel  to  each  other  and  to 
the  corneal  surface,  but  so  arranged  that  those  of  ad- 
jacent lamellae  cross  at  an  angle  of  about  twelve 
degrees. 

The  lamellae  are  also  cemented  to  each  other.    The 


THE  EYE. 


417 


corneal  cells  have  irregular  processes  and  lie  in  special 
cavities  called  corneal  spaces,  in  which  are  also  found 
a  varying  number  of  leucocytes.  These  spaces  seem 
to  be  part  of  a  complicated  lymphatic  system,  and 
communicate  with  each  other  by  means  of  a  complex 
system  of  canals.  While  blood  does  not  irrigate  the 
cornea,  lymph  does,  freely  and  extensively.  The 
posterior  elastic  or  Descemet's  membrane  resembles  the 


Lymph  cannliculi. 
% 


Corneal  space. 


Fig.  288.— Corneal  spaces  of  a  dog  (Bohm  and  Davidoff). 

anterior  elastic  membrane,  and  may  be  separated 
into  shreds  of  fine,  elastic,  connective-tissue  fibrils. 
The  endothelium  of  Descemet's  membrane  is  com- 
posed of  low,  hexagonal  cells  forming  a  single  layer. 
It  will  be  found  that  Descemet's  membrane  with  its 
investing  endothelium  is  reflected  to  form  the  an- 
terior layer  of  the  iris,  enclosing  therefor  the  anterior 
portion  of  the  aqueous  chamber. 
27 


41 8      NORMAL  HISTOLOGY  AND   ORGANOGRAPHY. 

TUNICA  MEDIA. 

i.  The  Choroid  Coat. — The  choroid  is  the  vascular 
tunic  of  the  eye,  and  may  be  divided  into  four  layers. 
From  without  inward  these  are  named:  i,  lamina 
suprachoroidea ;  2,  lamina  vasculosa  Halleri;  3, 
lamina  choriocapillaris ;  4,  glassy  layer,  or  vitreous 
membrane.  This  entire  tunic  is  derived  from  the 


Solera.  . 


Lamina  supra- 
choroidea. 


Lamina  vascu- 
losa Halleri. 


Lamina  chorio- 
capillaris. 
Glassy  layer. 

Fig.  289. — Section  through  the  human  choroid  (Bohm  and  Davidoff). 

mesoderm  and  is  largely  composed  of  connective- 
tissue  elements. 

The  Lamina  Suprachoroidea. — This  layer  is  closely 
applied  to  the  sclera,  and  is  composed  of  a  loose 
fabric  of  areolar  tissue  in  whose  meshes  are  con- 
nective-tissue cells  and  lymph  spaces  lined  with 
endothelium,  known  as  perichordeal  lymph  spaces. 


THE  EYE. 


419 


Pigment  cells  are  also  present.  The  lamina  vascu- 
losa  is  the  broadest  layer  and  is  also  composed  of 
areolar  tissue.  The  blood-vessels  constitute  its 
principal  portion,  and  they  are  so  distributed  that  the 
larger  ones,  the  veins,  occupy  its  outer  portions. 
The  lamina  choriocapillaris  consists  chiefly  of  capil- 


Lens. 


Anterior  epithelium. 
Iris. 


Pars  ciliaris  iridical. 


Cornea, 


Canal  of  Petit. 


Processus 
ciliares. 


Canal  of  Schlemm. 

Ciliary  muscle. 


Conjunctiva. ' 
Fig.  290. — Section  through  the  ciliary  body. 

lary  vessels  that  are  particularly  abundant  in  the 
region  of  the  macula  lutea,  or  yellow  spot  of  the 
retina.  In  other  respects  this  layer  resembles  the 
lamina  suprachoroidea,  except  that  pigment  cells 
are  absent.  The  glassy  or  vitreous  membrane  is  but 
2  fi  thick,  homogeneous,  clothes  the  inner  choroid 


420       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

surface,  and  also  forms  a  lining  membrane  against 
which  the  pigment  cells  of  the  retina  are  applied. 

2.  The  Ciliary  Body. — The  ciliary  body  is  that  por- 
tion of  the  tunica  media  extending  between  the  ora 
serrata  of  the  retina  and  the  base  of  the  iris.     On  the 
inner  surface  of  this  body  there  are  about  seventy 
meridional  folds  called  the  ciliary  processes.     Second- 
ary folds  and  processes  appear  on  and  between  the 
primary  folds,  while  the  whole  surface  is  clothed 
with  two  rows  of  epithelial  cells,  the  pars  ciliaris 
retina.     Of   these   the  outer   layer   is   deeply  pig- 
mented  and  represents  the  outer  layer  of  the  second- 
ary  optic   vesicle,   while   the   inner   layer   is   non- 
pigmented  and  develops  from  the  inner  layer  of  the 
optic  vesicle.     The  greater  bulk  of  the  ciliary  body 
is  made  up  of  smooth  muscle  tissue  called  the  ciliary 
muscle,  or  muscle  of  accommodation.     This  muscle 
may  be  divided  into  three  portions.     The  outer  por- 
tion is  made  up  of  meridional  fibers.     The  middle 
division  of  radial  fibers  have  their  origin  near  the 
canal  of  Schlemm,  from  which  they  spread  out  like 
a  fan.     The  inner  portion  is  near  the  base  of  the  iris 
and  the  fibers  are  circular.     The  combined  action  of 
these  fibers  is  to  pull  the  choroid  coat  forward  and 
inward  and  thus  slacken  the  tension  on  the  suspen- 
sory ligament  of  the  lens,  as  this  ligament  joins  with 
the  epithelial  cells  of  the  ciliary  body  as  well  as  with 
the  hyaloid  membrane  that  encloses  the  vitreous 
humor.     Under   this    condition   the   lens   becomes 
more  convex  and  the  eye  is  focused  to  near  objects. 

3.  The  Iris. — The  iris  is  a  pigmented  circular  cur- 
tain that  occludes  the  rays  of  light  from  the  periphery 


THE  BYE.  421 

of  the  lens.  The  circular  opening  in  the  iris  is  the 
pupil.  Three  layers  may  be  recognized  in  the  iris, 
enumerated  from  before  backward,  as  follows:  i 
anterior  endothelium;  2,  stroma  with  sphincter 
muscle ;  3 ,  pigment  epithelium,  or  pars  iridica  retinae. 
The  anterior  endothelium  is  a  single  layer  of  cells  that 
is  continuous  with  the  posterior  endothelium  of  the 
cornea.  The  stroma  forms  the  bulk  of  the  iris  and 
is  very  vascular  and  muscular.  Large  pigment  cells 
are  present  and  a  fine  reticular  tissue.  Smooth 
muscle  fibers,  the  sphincter  muscle  of  the  pupil, 
encircle  the  pupil.  Along  the  posterior  surface 
radial  fibers  probably  function  as  a  dilator  muscle 
of  the  pupil.  The  posterior  epithelium,  or  pars 
iridica  ciliaris,  is  a  direct  continuation  of  the  pars 
ciliaris  retinae  and  extends  to  the  margin  of  the  pupil. 
It  is  composed  of  two  layers  of  cells  and  both,  in  this 
case,  are  pigmented. 

TUNICA  INTERNA* 

The  inner  tunic  is  the  retina  of  the  eye,  which  may 
be  divided  into  ten  layers,  named  from  within  out- 
ward as  follows  : 

1 .  Internal  limiting  membrane. 

2.  Layer  of  nerve  fibers. 

3.  Ganglion  cell  layer. 

4.  Inner  molecular  layer. 

5.  Inner  nuclear  layer. 

6.  Outer  molecular  layer. 

7.  Outer  nuclear  layer. 

8.  External  limiting  membrane. 

9.  Rods  and  cones. 
10.  Pisment  laver. 


422      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 


(i)  The  internal  limiting  membrane  is  a  very  deli- 
cate homogeneous  layer  formed  by  lateral  expansions 
of  processes  of  neuroglia  elements.  It  is  closely  ap- 
plied to  (2)  the  optic  nerve  fibers.  The  latter  are  non- 
medullated  and  radiate  toward  the  entrance  of  the  op- 
tic nerve,  composed  of  both  centrifugal  and  centrip- 
etal axones.  The  latter  arise  from  (3)  the  ganglionic 
cells,  that  are  irregularly  distributed  along  the  inner 


r/S>  4Urf«  '@a  '9'4*&av<Bk  &'&. 


,  Internal  limiting  membrane. 
Layer  of  nerve  fibers. 
Ganglion  cell  layer. 

Inner  molecular  layer. 

Inner  nuclear  layer. 
Outer  molecular  layer. 


Outer  nuclear  layer. 

External  limiting  membrane. 
.-  Rods  and  cones. 

Pigment  layer. 

Fig.  291. — Section  of  retina  of  the  eye. 

border  of  the  retina.  These  cells  are  large,  multi- 
polar,  and  their  dendrites  extend  outward  and  con- 
tribute to  the  substance  of  (4)  the  inner  molecular 
layer.  The  latter  is  a  network  of  neuroglia  fibrils 
and  nerve  processes,  contributed  in  part  by  the  cells 
of  (5)  the  inner  nuclear  layer.  This  layer  is  com- 
posed of  several  rows  of  nucleated  cells  of  which  some 
are  sustentacular,  or  neuroglia  elements,  some  bi- 
polar ganglion  cells,  and  others  multipolar  ganglion 


THE  EYE. 


423 


cells  situated  in  the  outer  region  of  this  layer  and 
expanding  in  a  horizontal  direction.  (6)  The  outer 
molecular  layer,  like  the  inner  molecular,  is  a  net- 
work of  fibrils,  processes  from  all  the  ganglion  cells 
of  the  retina  and  also  neuroglia  elements.  The  ex- 
ternal portion  of  this  molecular  layer  is  not  so  densely 
packed  with  fibrils  and  has  been  called  Henle's  fiber 
layer.  (7)  The  outer  nuclear  layer  is  composed  of 
many  compact  rows  of  nuclei  and  is  the  most  con- 
spicuous layer  in  stained  sections  of  the  retina.  The 
cell  bodies  enclosing  most  of  these  nuclei  are  the 
visual  units  of  the  eye  and  are  called  rod-visual  and 
cone-visual  cells,  as  the  rods  and  cones  are  merely 
processes  of  these  cells.  The  cells  are  elongated  units 
whose  long  axis  is  placed  radial  to  the  eye,  and  whose 
multiple  processes  enter  the  outer  molecular  layer 
as  already  mentioned.  The  cone- visual  cells  are 
least  numerous  and  their  nuclei  are  placed  at  regular 
intervals  in  the  outer  portion  of  the  layer.  Their 
nuclei  are  somewhat  larger  than  the  nuclei  of  the 
other  cells.  Rod-like  neuroglia  elements  give  sup- 
port to  the  visual  cells.  (8)  The  external  limiting 
membrane  invests  the  outer  nuclear  layer.  It  is  a 
thin,  transparent,  homogeneous  membrane,  derived 
from  the  neuroglia  tissue,  and  forming  a  dividing  line 
between  the  rods  and  cones  and  the  outer  nuclear 
layer.  (9)  The  rods  and  cones  are  processes  from  the 
visual  cells  whose  nuclei  form  the  bulk  of  the  outer 
nuclear  layer.  The  rods  are  40  //  to  50  p.  in  length, 
and  consist  of  two  segments,  the  outer  being  doubly 
refractive  to  light,  and  may  be  separated  into  numer- 
ous transverse  discs  by  the  action  of  certain  reagents. 


424      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

The  inner  segment  shows  a  superficial  longitudinal 
striation,  due  to  impressions  from  fiber  baskets  of  the 
neuroglia  network.  The  cone  is  15  n  to  25  //  long 
and  its  inner  segment  considerably  broader  than  the 
rod.  The  rods  are  more  numerous  than  the  cones, 
three  or  four  of  the  former  intervening  between  two 
of  the  latter.  (10)  The  pigment  layer  forms  a  com- 
pact background  to  the  rods  and  cones.  It  consists 
of  hexagonal  cells  that  contain  black  pigment  gran- 
ules. The  inner  surfaces  of  these  cells  possess  thread- 
like filaments  that  interlace  between  the  rods  and 
cones.  The  nuclei  of  these  cells  lie  in  the  outer  ends 
of  these  cells,  the  so-called  basal  plates,  and  are  not 
pigmented.  The  granules  are  mobile  and  their  dis- 
tribution in  the  cells  varies  according  to  the  illumi- 
nation of  the  retina.  In  strong  light  the  pigment  is 
evenly  distributed  throughout  the  cytoplasm,  while 
in  weak  light  it  is  collected  at  the  outer  portion  of 
each  cell.  This  single  row  of  pigment  cells  represents 
the  outer  layer  of  the  primary  optic  vesicle,  while 
the  other  nine  layers  of  the  retina  develop  from  the 
inner  layer  of  this  vesicle. 

The  neuroglia  elements  of  the  retina  differ  from, 
those  of  the  brain  in  that  they  form  radial  sustentac- 
ular  fibers,  called  fibers  of  Mliller,  which  penetrate 
the  retina  to  the  rods  and  cones.  Each  fiber  repre- 
sents a  modified  epithelial  cell  which  terminates  in 
basal  plates,  the  latter  forming  the  limiting  mem- 
branes of  the  retina.  The  end  plates  that  form  the 
external  limiting  membrane  give  off  externally  short, 
inflexible  fibrils,  which  form  fiber-baskets  enclosing 
the  basilar  portions  of  the  rods  and  cones.  The 


THE  EYE.  425 

bodies  of  Miiller's  fibers  are  very  plastic  and  adjust 


themselves  to  the  pressure  exerted  by  the  various 


426      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

elements  that  constitute  the  different  layers  of  the 
retina  through  which  they  pass. 

In  certain  areas  of  the  retina  there  are  peculiar- 
ities that  differ  from  the  above  description.  These 
areas  are:  (i)  the  macula  lutea,  or  yellow  spot; 
(2)  the  optic  papilla,  or  blind  spot;  (3)  the  ora  ser- 
rata;  (4)  the  pars  ciliaris  retinae ;  (5)  the  pars  iridica 
retinae. 

i.  The  macula  lutea,  or  yellow  spot,  is  a  crater- 
like  area  of  the  retina  that  lies  in  the  visual  axis  of 

Fovea  centralist 

Layer  of 
nerve  fibers. 

Ganglion  cell' 
layer. 

Inner  molecu- 
lar layer. 

Inner  nuclear 
layer. 

Outer  molecu-  . 
lar  layer. 

Outer  fibrous 
layer. 

Outer  nuclear 
layer. 

Cones. 

Fig.  293. — Section  through  human  macula  lutea  and  fovea  centralis. 
As  a  result  of  treatment  with  certain  reagents,  the  fovea  centralis  is  deeper 
and  the  margin  more  precipitous  than  during  life  (Bohm  and  DavidofT). 


the  eye.  The  central  depression  is  called  the  fovea 
centralis.  Its  margin  is  somewhat  thickened  and 
presents  all  the  layers  of  the  retina,  while  in  the  fovea 
the  layers  are  practically  reduced  to  the  cone-visual 
elements.  From  this  center  the  cell  bodies  of  the 
cones  radiate  in  curves  to  reach  the  outer  molecular 
layer,  which  gives  rise  to  obliquely  directed  fibers 
known  as  Henle's  fiber  layer.  The  macula  lutea  is 
the  most  sensitive  spot  in  the  retina  and  derives  its 


THE  EYE.  427 

name  from  the  yellow  pigment  held  in  solution  within 
the  cell  layers. 

2.  The  optic  papilla,  or  blind  spot,  is  the  point  of 
entrance  of  the  optic  nerve.  It  is  found  a  little  to 
the  nasal  side  of  the  macula  lutea.  From  the  center 
of  this  papilla  the  nerve  fibers  spread  out  radially  to 
supply  the  various  parts  of  the  retina.  The  optic 
fibers  lose  their  medullary  sheaths  in  their  passage 
through  the  sclera  and  the  choroid,  so  that  the  optic 
nerve  at  this  point  becomes  suddenly  thinner.  Be- 

Physiologic  excavation. 

Layer  of  nerve  fibers*    _^— — - -" 

Inner  molecular  layer^l 

Inner  nuclear  layer-\.J 

Outer  molecular  layer. o- 

Outer  nuclear  layer  *~~. 

Rods  and  cones.  -' 

Pigment  layer.  •' 


Sclera.... 
Lamina  cribrosa.  ••' 


ILL 


Fig.  294. — Section  through  point  of  entrance  of  human  optic    nerve 
(Bohm  and  Davidoff). 


cause  of  this  and  the  fact  that  the  fibers  curve  radi- 
ally, there  is  produced  a  deep  circular  depression  in 
this  region.  At  this  point  the  retina  is  absent,  the 
choroid  coat  is  interrupted,  while  connective-tissue 
fibers  of  the  sclera,  called  the  lamina  cribrosa,  inter- 
lace and  cross  the  optic  fibers. 

3.  The  or  a  serrata  is  that  portion  of  the  retina  that 
marks  the  posterior  limit  of  the  ciliary  body.  ^  At 
this  point  there  is  a  rapid  diminution  of  the  retinal 
layers  until  but  two  rows  of  cells  remain,  the  outer 
one  pigmented.  The  optic  fibers  and  visual  cells 


428       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

disappear  first.  Then  the  outer  molecular  layer  is 
lost,  so  that  the  nuclear  layers  become  confluent. 
Ultimately  but  two  rows  of  cells  remain,  which  are 
continued  over  the  ciliary  body  as  the  pars  ciliaris 
retina,  already  mentioned  in  the  description  of  the 
ciliary  body.  The  ora  serrata  forms  a  zigzag  line 
which  marks  the  posterior  border  of  the  ciliary  folds. 
The  iridica  retina  has  already  been  described  in 
connection  with  the  description  of  the  iris. 

REFRACTING  MEDIA. 

The  refracting  media  of  the  eye  are  the  cornea, 
aqueous  humor,  lens,  and  the  vitreous  humor.  The 
cornea  is  described  on  another  page. 

i.  The  aqueous  humor  is  a  structureless  fluid  re- 
sembling lymph  that  fills  the  chamber  of  the  eye  in 
front  of  the  lens.  The  iris  is  suspended  in  this  fluid 
and  divides  the  chamber  into  an  anterior  and  a 
posterior  compartment.  The  fluid  is  largely  a  se- 
cretion from  epithelial  cells,  or,  according  to  some, 
from  epithelial  glands  said  to  be  located  in  the  region 
of  the  ciliary  body.  The  aqueous  humor  is  re- 
placed if  accidentally  lost. 

2.  The  Lens. — The  origin  of  the  lens  has  already 
been  described  as  an  ectodermal  invagination  in  the 
form  of  a  vesicle.  The  cells  of  the  posterior  wall  of 
this  vesicle  form  the  bulk  of  the  lens.  These  cells 
become  long  and  slender  and  are  known  as  the  lens 
fibers,  while  the  cells  of  the  anterior  wall  remain  low 
and  cubical  and  form  the. anterior  epithelium  of  the 
lens.  Surrounding  the  lens  on  all  sides  is  the  lens 
capsule.  This  capsule  is  a  homogeneous  membrane, 


THE  EYE. 


429 


thicker  on  the  anterior  surface  of  the  lens  than  on  the 
posterior,  and  with  certain  reagents  appears  to  be 
made  up  of  lamellae.  The  latter  connect  with  fibers 
of  the  suspensory  ligament. 

In  adults  the  anterior  epithelium  forms  a  single 
layer  of  flattened  or  cubical  cells  which  extend  as  far 


Anterior  capsule. 

Anterior  epithelium 
Lens  fibers. 


Fig.  295.— Crystalline  lens:    A,  longitudinal  fibers;  B,  posterior  surface 
view  of  anterior  epithelium  (Leroy). 

as  the  equatorial  margin  of  the  lens.  At  this  mar- 
gin the  cells  increase  in  height  to  form  the  lens  fibers. 
These  are  flattened  hexagonal  prisms,  thickened  at 
the  posterior  ends.  They  pass  in  a  meridional  direc- 
tion from  the  anterior  surface  backward,  and  are 


430       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

held  together  by  a  small  amount  of  cement  sub- 
stance. 

The  suspensory  ligament  connects  the  capsule  of  the 
lens  with  the  epithelium  of  the  ciliary  body  and  the 
hyaloid  membrane  of  the  vitreous  humor.  From 
this  point  the  fibers  pass  forward  and  inward  to  be- 
come inserted  into  the  capsule  of  the  lens.  The  in- 
sertion occupies  a  wide  zone  at  the  equator  of  the 
lens,  which  reaches  some  distance  on  the  anterior  and 
posterior  surfaces.  Between  these  fibers  there  is 
consequently  a  canal  around  the  lens,  divided  by 
septa,  the  canal  of  Petit,  which  communicates  by 
minute  openings  with  the  anterior  chamber. 

3.  The  vitreous  humor  fills  the  chamber  of  the  eye 
back  of  the  lens.  It  is  a  transparent  tissue  that 
contains  about  98  per  cent,  of  fluid  substance  and 
fine  interlacing  fibers,  as  well  as  a  few  connective- 
tissue  cells  and  leucocytes.  Toward  the  surface  the 
fibers  are  more  densely  arranged,  forming  the  hyaloid 
membrane  which  encloses  the  entire  vitreous  body. 
The  origin  of  the  vitreous  humor  has  been  described 
in  connection  with  the  developmental  history  of  the 
eye. 

BLOOD-VESSELS  OF  THE  EYE. 

The  arteries  of  the  choroid  are  derived  from  the 
short  posterior  ciliary,  the  long  ciliary,  and  the  an- 
terior ciliary  arteries.  The  short  posterior  penetrate 
the  sclera  in  the  vicinity  of  the  optic  nerve,  and 
supply  blood  to  the  choroid  of  that  region.  These 
arteries  also  anastomose  with  branches  from  the 
retinal  vessels.  The  long  posterior  ciliary  penetrates 


THE  EYE. 


431 


the  sclera  near  the  optic  nerve,  and  course  forward 
between  the  choroid  and  the  sclera  to  the  ciliary 
body.  It  supplies  blood  to  the  ciliary  muscles,  the 
ciliary  processes,  and  the  iris.  The  anterior  ciliary 
arteries  lie  close  to  the  straight  ocular  muscles  and 
penetrate  the  sclera  near  the  sclerocorneal  junction. 
They  give  off  branches  to  the  iris  and  the  ciliary  body, 
anastomosing  with  branches  from  the  long  posterior 
ciliary  artery.  Veins  return  the  blood  from  these 
regions  and  bear  the  same  names  as  the  arteries 
they  accompany. 


Ocular  muscle. 


Sclera. 
Choroid. 


Ciliary  muscle. 
Iris. 

Conjunc.  cul-de-sac. 

Ant.  chamber  and 

aqueous  humor. 

Crystalline  lens. 

Posterior  chamber. 

Angle  of  ant.  chamber. 

Suspensory  ligament 

of  the  lens. 


Retina. 

Optic 

nerve  with 

central 

retinal 

artery. 
Ocular 

muscle. 


Cornea.  Vitreous  chamber. 

Fig.  296. — Vertical  section  through  the  eyeball  and  lids  (Pyle). 

The  retina  is  supplied  with  blood  from  a  central 
artery  and  vein  that  enter  and  leave  the  retina  at  the 
optic  papilla,  or  blind  spot.  Each  divides  into  a 
superior  and  inferior  papillary  artery  and  vein.  The 
latter  again  divide  into  two  branches,  making  in  all 
four  arteries  and  four  veins  known  according  to  their 
position  as  superior  and  inferior  nasal,  and  superior 
and  inferior  temporal  vessels.  Within  the  retina 


432     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

itself  a  coarse  plexus  of  vessels  blends  with  the  nerve 
fiber  layer.     This  connects  with  a  fine  network  lying 


Non-striated  muscle  fibers  of  the  tar  sal  muscle  and 
tendon  of  the  levator  palpebra  super  ioris. 


Lymph  node 
of  the  con- 
junctiva 
palpebrce. 
Accessory 
lacrimal 
gland. 


Tarsus. 


Meilomian 
gland. 

Arterial   ar- 
cus  tarseus. 

Excretory 

duct  of 

Meibomian 

gland. 


M .  orbicu- 
Laris  pal- 
Pebrarum 


Ciliary 
gland 
(Moll). 


Ciliary 
gland 
(Moll). 

Ciliary  muscle  of  Riolani.  Cilia. 

Fig.  297. — Vertical  section  of  the  upper  eyelid  of  man  (Sobotta.) 


within  the  inner  nuclear  layer      The  visual  cell  layer 
is  non- vascular. 


THE  BYE. 


The  eyelids  are  two  movable  folds 
of  the  skin  whose  inner  surface  is 
covered  by  a  mucous  membrane, 
the  conjunctiva.  The  skin  on  the 
outer  surface  is  thin,  movable,  and 
presents  fine  hairs  with  small  seba- 
ceous glands,  and  also  a  few  sweat 
glands.  At  the  lid  margin  papillae 
are  developed  and  the  epidermis  is 
thickened.  Along  the  outer  bor- 
der there  are  two  or  three  rows  of 
large  hairs,  the  eyelashes,  the  poste- 
rior row  of  which  possesses  seba- 
ceous glands  and  modified  sweat 
glands,  called  the  glands  of  Moll. 
The  eyelids  are  further  provided 
each  with  twenty-five  to  thirty 
large  glands,  known  as  Meibomian 
or  tarsal  glands,  whose  ducts  open 
on  the  palpebral  margin  just  in- 
ternal to  the  eyelashes.  Each 
gland  has  a  large  central  duct  lined 
by  stratified  epithelium  and  into 
which  numerous  branched  alveoli 
open.  The  latter  resemble  the  al- 
veoli of  sebaceous  glands.  The 
Meibomian  glands  lie  close  to  the  in- 
ternal surface  of  the  eyelids  and 
their  cells  undergo  a  fatty  change 
and  give  out  a  fat-containing  secre- 
tion. 

In  each  lid  there  exists  a  frame- 
28 


Fig.  298.— Mei- 
bomian or  ,  tarsal 
gland,  reconstructed 
after  Bern's  wax- 
plate  method  (Hu- 
her). 


434      NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

work  of  condensed  fibrous  tissue,  which  gives  con- 
sistency  and  shape  to  the  lid,  and  is  termed  the  tar- 
sal  plate,  or  tarsus.  The  orbicularis  oculi  muscle  lies 
beneath  the  subcutaneous  tissue  of  the  outer  surface 
and  is  composed  of  voluntary  muscle  fibers  that  arch 
between  the  angles  of  the  eyelids. 


Fig.  299. — Lacrimal  and  Meibomian  glands,  the  latter  viewed  from 
the  posterior  surface  of  the  eyelids.  (The  conjunctiva  of  the  upper  lid 
has  been  partially  dissected  off,  and  is  raised  so  as  to  show  the  Meibomian 
glands  beneath.)  I,  Free  border  of  upper,  and  2,  free  border  of  lower  lid, 
with  openings  of  the  Meibomian  glands;  5,  Meibomian  glands  exposed, 
and  6,  as  seen  through  conjunctiva;  7,  8,  lacrimal  gland;  9,  its  excretory 
ducts,  with  10,  their  openings  in  the  conjunct! val  cul-de-sac;  II,  con- 
junctiva (Testut). 

The  conjunctiva  is  a  mucous  membrane  that  lines 
the  inner  surface  of  the  eyelids  and  is  reflected  over 
the  front  of  the  eye.  Over  the  cornea  it  forms  the 
anterior  stratified  epithelium,  and  has  already  been 
described.  The  line  along  which  it  is  reflected  on  to 
the  globe  of  the  eye  is  called  the  fornix.  The  pal- 


THE  EYE. 


435 


pebral  portion  adheres  intimately  to  the  tarsal  plate 
and  presents  numerous  papillae.  It  is  covered  by  a 
layer  of  columnar  cells  beneath  the  bases  of  which 
are  small  flattened  cells.  Goblet  cells  are  to  be  found 
among  these  cells.  Over  the  globe  of  the  eye  it  ad- 
heres closely  to  the  sclera,  and  this  portion  of  the 
conjunctiva  is  perfectly  smooth  and  is  composed  of 
stratified  squamous  epithelium.  The  conjunctiva 
that  clothes  the  eyelid  is  thinner  than  that  which 
covers  the  cornea  and  any  for- 
eign particle,  therefore,  tends 
to  cling  to  the  eyelid  rather 
than  to  the  eye. 

The  Lacrimal  Apparatus. — 
This  consists  of  (i)  the  lacri- 
mal  or  tear  gland,  (2)  the  lac- 
rimal  canals,  and  (3)  lacrimal 
sac,  or  nasal  duct. 

The  lacrimal  gland  is  a 
branched  tubular  gland  situ- 
ated in  the  upper  and  outer 
part  of  the  orbital  cavity.  Its 
structure  resembles  that  of  a 

serous  gland.  The  ducts,  which  are  numerous,  are 
clothed  with  stratified  epithelium  and  open  on  the 
conjunctival  surface,  over  which  the  secretion  is 
evenly  distributed  by  the  action  of  the  eyelids. 

The  lacrimal  canals  begin  as  two  minute  orifices 
at  the  apices  of  the  papillae  lacrimales  situated  near 
the  inner  canthus.  They  are  lined  by  stratified 
epithelium  and  open  directly  into  the  lacrimal  sac. 
The  latter  is  lined  with  simple  pseudostratified  epi- 


Fig.  300. — i,  Canalicu- 
lus;  2,  lacrimal  sac;  3,  na- 
sal duct;  4,  plica  semilu- 
naris;  5,  caruncula  lacri 
malis  (Leidy). 


436     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

thelium,  having  two  strata  of  nuclei,  and  represents 
the  upper  expanded  portion  of  the  nasal  duct. 
This  duct  has  a  similar  epithelium  and  opens  into 
the  inferior  meatus  of  the  nose.  Ciliated  epithelium 
has  been  described  as  being  present  in  the  nasal  duct, 
and  also  mucous  glands  in  the  lower  parts. 


CHAPTER  XV. 
THE  ORGAN  OF  HEARING. 

The  organ  of  hearing  consists  of  three  portions,— 
external,  middle,  and  internal  ear,  the  last  being  the 
essential  part,  as  within  this  are  the  peripheral  termi- 
nations of  the  auditory  nerve. 

i.  The  External  Ear. — The  pinna  or  auricle  pro- 
jects from  the  side  of  the  head  and  is  covered  with  a 
thin  layer  of  skin,  in  which  are  found  hairs,  sebaceous 
glands,  and  sweat  glands.  A  cartilage  matrix  of 
this  portion  is  of  the  elastic  variety  with  interposed 
areas  of  non-elastic  cartilage.  The  lower  lobe  is  free 
from  cartilage  and  is  composed  of  adipose  tissue. 
The  external  auditory  meatus  is  the  passage  leading 
inward  from  the  concha  as  far  as  the  tympanic  mem- 
brane. Its  average  length  is  about  one  inch.  This 
tube  may  be  divided  into  an  external  cartilaginous 
portion  and  an  internal  osseous  portion.  The  skin 
lining  the  cartilaginous  portion  is  clothed  with  coarse 
hairs  and  possesses  modified  sweat  glands  called 
ceruminous  glands.  These  are  branched,  of  the 
tubulo-alveolar  variety,  and  empty  into  hair  fol- 
licles near  the  surface  of  the  skin,  or  on  the  surface 
of  the  skin  in  the  neighborhood  of  the  hair  follicles. 
The  skin  of  the  osseous  portion  is  supplied  with 
neither  hair  nor  glands,  but  possesses  slender  papillae. 

437 


438     NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 


Helix. 


At  the  bottom  of  the  auditory  canal  is  the  tympanic 
membrane.  It  is  an  elliptical  disc  placed  at  an  ob- 
lique angle  to  the  ear  canal,  with  its  antero-inferior 
border  most  distant  from  the  outer  orifice.  This 
membrane  is  composed  of  three  layers,  an  external 
cutaneous,  a  middle  fibrous,  and  an  inner  mucous. 
The  external  layer  is  continuous  with  the  integu- 
mentary lining  of  the  meatus  and  consists  of  a  thin 
layer  of  cutis  covered  by  epidermis.  The  middle 
layer,  or  membrana  propria,  consists  of  two  sets  of 

fibers, — external  or 
radial  fibers  next  to 
the  integument,  and 
internal  or  circular 
fibers  next  to  the  in- 
ner mucous  lining. 
The  circular  fibers 
are  numerous  near 
the  circumference 
but  scattered  and 
few  in  number  near 
the  center.  In  the 
upper  and  anterior  margin  of  the  membrane  is  a 
small  triangular  area  that  is  thin  and  lax  and  is 
called  the  pars  flaccida.  The  main  portion  of  the 
membrane  is,  on  the  other  hand,  tightly  stretched 
and  termed  the  pars  tensa.  Both  radial  and  circular 
fibers  are  absent  from  the  pars  flaccida. 

2.  The  Middle  Ear. — The  middle  ear,  or  tympanic 
cavity,  is  a  small  air  chamber  in  the  tympanic  bone, 
intervening  between  the  inner  end  of  the  external 
auditory  meatus  and  the  outer  wall  of  the  internal 


Fossa  of 

helix. 
Anthelix. 


Concha. 


Antitragus. 


Fig.  301. — External  ear   (Randall). 


THE   ORGAN   OF   HEARING. 


439 


ear  or  labyrinth.  It  is  lined  by  a  mucous  membrane 
and  contains  the  bones  of  the  ear,  malleus,  incus,  and 
stapes.  The  mucous  membrane  is  folded  over  these 
ossicles  and  has  a  pseudostratified  ciliated  epithe- 
lium, having  two  strata  of  nuclei.  Cilia  are,  how- 
ever, absent  on  the  surface  of  the  auditory  ossicles, 
their  ligaments,  and  the  tympanic  membrane.  The 


Fig.  302. — Semidiagrammatic  section  through  the  right  ear:  G,  Exter- 
nal,auditory  meatus;  Tt  membrana  tympani;  P,  tympanic  cavity;  o, 
fenestra  ovalis;  r,  fenestra  rotunda;  B,  semicircular  canal;  S,  cochlea; 
VI,  scala  vestibuli;  Ptt  scala  tympani  (Czermak.) 

tympanic  cavity  communicates  with  the  mouth  by 
a  narrow  canal,  the  Eustachian  tube,  which  transmits 
air  and  conveys  mucous  secretion  from  the  middle 
ear.  This  tube  is  about  one  and  one-half  inches  in 
length  and  is  directed  downward  and  inward  from 
the  anterior  part  of  the  tympanum  to  open  on  the 


440       NORMAL   HISTOLOGY  AND   ORGANOGRAPHY. 


upper  part  of  the  nasopharynx  by  a  wide  orifice. 
Its  anterior  part,  about  one  inch  in  length,  is  enclosed 
in  cartilage,  while  its  posterior  portion  is  encased  in 
bone.  The  mucous  membrane  is  ciliated  and  glands 
are  absent. 

3.  The  Internal  Ear. — The  internal  ear  is  the  es- 
sential part  of  the 
organ  of  hearing 
and  consists  of  a 
bony  and  a  mem- 
branous labyrinth. 
The  latter  is 
contained  within 
the  former  and 
represents  the 
same  general 
shape,  the  two 
being  separated 
by  a  lymph  space 
containing  the 
perilymph.  A  se- 
ries of  cavities 
constitute  the 
bony  labyrinth, 
which  are  named 
from  before  back- 
wards— cochlea,  -vestibule,  and  semicircular  canals. 
The  membranous  labyrinth  situated  within  these 
cavities  consists  of  the  membranous  cochlea,  utriculus, 
and  sacculus,  and  membranous  semicircular  canals. 

(i)   Vestibule,  Utriculus,  and  Sacculus. — The  vesti- 
bule forms  the  central  portion  of  the  bony  labyrinth 


Fig.  303. — Otoscopic  view  of  left 
membrana  tympani  :  i,  Membrana  flac- 
cida;  2,  2',  folds  bounding  the  former; 
3,  reflection  from  processus  brevis  of 
malleus;  4,  processus  longus  of  incus 
(occasionally  seen);  5,  membrana  tym- 
pani; 6,  umbo  and  end  of  manubrium; 
7,  pyramid  of  light  (Morris). 


THE   ORGAN    OF   HEARING.  441 

and  communicates  behind  with  the  bony  semicircu- 
lar canals,  and  in  front  with  the  cochlea.  Its  outer 
wall  forms  the  inner  wall  of  the  tympanic  cavity, 
and  in  it  is  seen  the  fenestra  ovalis,  into  which  the 
foot  of  the  stapes  is  adjusted.  The  posterior  part 
of  the  vestibule  receives  five  apertures  that  lead  to 
the  semicircular  canals,  while  its  anterior  part  leads 
by  an  elliptical  opening  into  the  scala  vestibuli  of  the 
cochlea. 


Superior  semicircular  canal. 


Horizontal  semi- 
circular canal. 
Posterior  semi- 
circular canal. 


Ampulla.  ^£  ^mlGI*%-  ^ny  cochlea. 


Vestibule.  Fenestra  rotunda. 


Fig.  304. — Right  bony  labyrinth,  viewed  from  outer  side:  The  figure 
represents  the  appearance  produced  by  removing  the  petrous  portion  of 
the  temporal  bone  down  to  the  denser  layer  immediately  surrounding 
the  labyrinth  (from  Quain,  after  Sommering). 

The  utriculus  and  sacculus  are  two  sac-like  struc- 
tures enclosed  in  the  bony  vestibule.  The  two  are 
indirectly  connected  by  the  ductus  endolymphaticus , 
which  is  a  Y-shaped  channel  that  terminates  in  a 
blind  recess,  the  saccus  endolymphaticus.  The  latter 
lies  against  the  dura  on  the  posterior  surface  of  the 
temporal  bone. 

The  utriculus  is  larger  than  the  sacculus  and  occu- 


442       NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

pies  the  postero-superior  portion  of  the  bony  vesti- 
bule. It  communicates  by  five  apertures  with  the 
membranous  semicircular  canals.  Its  wall  is  com- 
posed of  fibrous  tissue,  lined  internally  with  a  single 
layer  of  columnar  epithelium.  The  floor  and  an- 
terior wall  is  thickened  to  form  the  macula  acustica 
utriculi,  which  is  innervated  by  fibers  of  the  auditory 
nerve.  The  epithelium  of  this  region  is  composed 


Auditory  nerve 
with  its  vestibu- 
lar  and  cochlear 
branches. 


Ant.  semicircular  canal. 
.Ampulla. 


Cochlear  duct. 


Canalis  reunienS.         Ductus        Ampulla.          Horizontal  semicir- 
endolymphaiicus.  cular  canal. 


Fig.  305. — Membranous  labyrinth  of  the  right  ear  from  five-months  hu- 
man embryo  (from  Schwalbe,  after  Retzius). 


of  two  kinds  of  cells:  (i)  slender  sustentacular  cells 
resting  on  a  basement  membrane,  and  (2)  hair  cells, 
or  auditory  cells.  The  latter  support  a  number  of 
stiff  hairs  and  constitute  the  neuro-epithelium, 
around  which  arborize  the  neurons  of  the  auditory 
nerve.  Crystals  of  calcium  carbonate,  known  as 
otoliths,  are  found  on  the  surface  of  the  epithelium. 
The  sacculus  occupies  the  lower  portion  and  fore 


THE    ORGAN    OF   HEARING.  443 

part  of  the  bony  vestibule.  It  is  oval  in  shape, 
smaller  than  the  utriculus,  its  longest  diameter 
measuring  about  3  mm.  From  its  lowest  part  a  short 
canal,  the  duct  of  Hensen,  opens  into  the  ductus 
cochlearis.  Anteriorly  there  is  an  oval,  whitish 
thickening,  the  macula  acustica  sacculi,  innervated  by 
the  neurons  of  the  auditory  nerve.  The  histology 
of  the  sacculus  is  like  that  of  the  utriculus. 

(2)  Semicircular  Canals. — There  are  three  osseous 
canals   situated   behind   and   above  the   vestibule. 
The  superior  canal  is  vertical,  the  external  is  hori- 
zontal, and  the  posterior  is  vertical.     They  open  into 
the  vestibule  by  five  apertures,  since  the  inner  ex- 
tremity of  the  superior  and  the  upper  extremity  of 
the  posterior    join  to  form  a  common  duct,  the 
canalis    communis.     Each    canal    presents    an    en- 
largement or  osseous  ampulla  near  its  origin  with 
the  vestibule.     The  membranous  semicircular  canals 
partly  fill  the  bony  canals,  to  which  they  conform. 
The  peripheral  border  of  each  canal  is  fixed  to  the 
periosteum  of  the  bony  canals  while  the  opposite  part 
is  free.     Each  canal  is  dilated  in  the  bony  ampulla 
to  form  a  membranous  ampulla.     These  canals  com- 
municate with  the  utriculus  and  possess  a  fibrous 
wall  clothed  with  simple  pavement  epithelium,  ex- 
cepting in  the  ampullae,  where  it  is  columnar.     In  the 
latter  slender  sustentacular  cells  intervene  between 
shorter  neuro-epithelial  cells,  or  hair  cells,  similar  to 
those  of  the  maculae.     The  neurons  of  the  auditory 
nerve  arborize  around  the  bases  of  the  hair  cells. 

(3)  The  Bony  and  Membranous  Cochlea. — The  bony 
cochlea  assumes  the  form  of  a  short  cone  and  con- 


444      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

sists  of  a  spirally  arranged  tube  which  forms  from 
two  and  one-half  to  two  and  three-quarter  coils 
around  a  central  pillar  termed  the  modiolus.  The 
length  of  this  tube  is  about  30  mm.  and  its  diameter, 
near  the  base  of  the  cochlea,  about  2  mm.  The 


Ligamen- 
tum 
spirale. 


Spiral 
ganglion. 


Osseous  cochlear  wall. 


Nervus  cochlearis. 


Fig.  306. — Longitudinal  section  of  the  cochlea  of  a  cat.  This  figure 
gives  a  general  view  of  the  cochlea.  The  cochlear  duct  is  met  with  six 
times  in  the  section  (Sobotta). 


modiolus  is  about  3  mm.  in  height  and  transmits  the 
nerve.  A  flat  shelf  of  bone,  the  lamina  spiralis, 
winds  around  the  modiolus  like  the  thread  of  a  screw, 
and  projects  about  half-way  into  the  cochlear  tube 
and  thus  incompletely  divides  this  tube  into  two 
passages,  of  which  the  upper  is  named  the  scala  vesti- 


THE   ORGAN    OF   HEARING. 


445 


buli,  and  the  lower  the  scala  tympani.  A  mem- 
brane— the  membrana  basilaris — stretches  from  the 
free  edge  of  the  bony  lamina  spiralis  to  the  outer 
wall  of  the  cochlea  and  completes  the  scala  vestibuli 


Fig-  3°7- — Section  through  one  of  the  turns  of  the  osseous  and  mem- 
branous cochlear  ducts  of  the  cochlea  of  a  guinea-pig:  /,  Scala  vestibuli; 
m,  labium  vestibulare  of  the  limbus;  n,  sulcus  spiralis  internus;  o,  nerve 
fibers  lying  in  the  lamina  spiralis;  p,  ganglion  cells;  q,  blood-vessels;  a, 
bone;  b,  Reissner's  membrane;  DC,  ductus  cochlearis;  d,  Cord's  mem- 
brane; /,  prominentia  spiralis;  g,  organ  of  Corti;  h,  ligamentum  spirale; 
i,  crista  basilaris;  k,  scala  tympani  (Bohm  and  Davidoff). 

and  the  scala  tympani,  but  the  two  communicate 
at  the  apex  of  the  cochlea.  The  scala  tympani 
begins  at  the  fenestra  rotunda,  in  the  inner  wall  of  the 


446      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

tympanum  just  below  the  fenestra  ovalis,  and  the 
scala  vestibuli  leads  to  the  perilymphatic  space  of 
the  vestibule.  The  fenestra  rotunda  is  closed  by 
the  tympanic  membrane. 

From  what  has  been  stated  it  is  evident  that  an 
injection  into  the  scala  tympani  through  the  fora- 
men rotunda  will  pass  into  the  scala  vestibuli  at  the 
apex  of  the  cochlea,  and  travel  down  the  passage 
above  the  lamina  spiralis  to  ultimately  reach  the 
perilymphatic  space  of  the  vestibule  and  exert  press- 
ure against  the  base  of  the  stapes  through  the  fenes- 
tra ovalis. 

The  membranous  cochlea  (ductus  cochlearis  or  scala 
media)  forms  a  spiral  canal  inside  the  bony  cochlea, 
and  ends  at  the  apex  of  the  latter  in  a  blind  ex- 
tremity, the  lagena.  This  scala  media  lies  near  the 
free  margin  of  the  lamina  spiralis  and  just  above 
the  membrana  basilaris.  It  thus  forms  a  spiral  tube 
that  gradually  increases  in  size  from  its  lower  to  its 
upper  or  distal  end.  Its  lower  end  communicates 
with  the  sacculus  through  the  ductus  reuniens  of 
Hensen.  Triangular  in  transverse  section  it  has  a 
roof,  called  Reissner's  membrane,  which  separates  it 
from  the  scala  vestibuli.  Its  outer  wall  is  the  peri- 
osteal  lining  of  the  bony  cochlea,  while  its  floor  is  the 
outer  border  of  the  lamina  spiralis  and  the  membrana 
basilaris.  This  membranous  labyrinth  is  clothed 
throughout  its  whole  length  by  a  single  layer  of 
epithelial  cells. 

Reissner's  membrane  consists  of  an  exceedingly 
thin  connective-tissue  lamella  lined  on  the  vestibular 
side  with  a  single  layer  of  endothelial  cells,  and  on  the 


THE   ORGAN   OF   HEARING. 


447 


duct   by   a  single   layer  of  flat  epithelial 


cochlear 
cells. 

The  outer  wall  of  the  scala  media  is  the  periosteal 
lining  of  the  bony  cochlea  which  is  thickened  and 
modified  to  form  what  is  termed  the  ligamentum 
spirale  cochlea.  The  ligament  has  a  projection,  the 
crista  basilaris,  to  which  the  outer  edge  of  the  mem- 
brana  basilaris  is  attached.  The  inner  surface  of 


a  b 

i 


c        d          I 


n 


P 


Fig.  308. — Organ  of  Corti:  At  oc  the  tectorial  membrane  is  raised;  c, 
outer  sustentacular  cells;  d,  outer  auditory  cells;  /,  outer  pillar  cells;  g, 
tectorial  membrane;  h,  inner  sustentacular  cells;  i,p,  epithelium  of  the 
sulcus  spiralis  internus;  k,  labium  vestibulare;  e,  tympanic  investing 
layer;  m,  outer  auditory  cells;  n,  n,  nerve  fibers  which  extend  through 
the  tunnel  of  Corti;  o,  inner  pillar  cell;  q,  nerve  fibers;  b,  b,  basilar  mem- 
brane; a,  epithelium  of  the  sulcus  spiralis  externus;^  r,  cells  of  Hensen; 
s,  inner  auditory  cell;  /,  ligamentum  spirale  (after  Retzius). 


this  wall  is  clothed  with  simple  epithelium  of  the 
columnar  type,  which  in  places  appears  to  be  strat- 
ified and  to  possess  darkly  granulated  cells. 

On  the  floor  of  the  scala  media  and  resting  on  the 
basilar  membrane  is  the  complicated  structure 
termed  the  organ  of  Corti.  This  consists  of  the  fol- 
lowing structures:  (i)  Corti 's  rods  or  pillars;  (2) 


448      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

hair  cells  (inner  and  outer) ;  (3)  supporting  cells  of 
Deiters ;  (4)  the  cells  of  Hensen  and  Claudius;  (5) 
the  lamina  reticularis,  and  (6)  a  cuticular  membrane, 
the  membrana  tectoria. 

1 .  The  rods  of  Corti  form  two  rows,  an  inner  and  an 
outer.     The  bases  of  the  two  rows  are  planted  on  the 
membrana  basilaris,  some  little  distance  apart,  and 
the  outer  ends  come  in  contact  so  that  between  the 
two  rows  above  and  the  basilar  membrane  below 
there  is  enclosed  a  triangular  tunnel,  the  tunnel  of 
Corti.     This   tunnel  increases   both   in   height   and 
width  toward  the  apex  of  the  cochlea.     The  inner 
rods  number  nearly  six  thousand.     The  outer  rods 
number  about  four  thousand,  and  are  longer  than  the 
inner.     They  are  also  more  inclined  toward  the  bas- 
ilar membrane  and  form  with  it  an  angle  of  about 
forty  degrees. 

2.  The  hair  cells  are  placed  on  each  side  of  the  rods 
and  thus  form  an  inner  and  an  outer  set.     The  inner 
hair  cells  form  a  single  row  and  number  about  three 
thousand  five   hundred,  so  that   each   cell  is   sup- 
ported by  a  little  more  than  one  rod.     Their  free  ex- 
tremities are  surmounted  by  about  twenty  fine  hair- 
like  processes  arranged  in  the  form  of  a  crescent. 
Each  cell  is  oval  and  contains  a  large  nucleus.     The 
lower  end  is  rounded  and  reaches  about  'half-way 
down  the  rod,  and  in  contact  with  this  end  are  the 
arborizations   of  the   nerve   terminations.     To   the 
inner  side  of  these  cells  are  several  rows  of  columnar 
cells  that  function  as  supports.     The  outer  hair  cells 
number  about  twelve  thousand,  and  form  three  rows 
in  the  basal  coil  and  about  four  rows  in  the  upper  two 


THE   ORGAN   OF   HEARING. 


449 


coils.  The  free  extremity  of  each  cell  supports  some 
twenty  hair-like  processes,  while  the  outer  extremity 
reaches  half-way  to  the  basilar  membrane  and  is  in 
contact  with  nerve  arborizations. 

3.  Deiters1  supporting  cells  alternate  with  the  rows 
of  the  outer  hair  cells.  Their  lower  ends  expand 
upon  the  basilar  membrane,  and  the  upper  end  tapers 


Fig.  309. — Section  of  Corti's  organ  from  guinea-pig's  cochlea:  ST, 
scala  tympani;  TC,  tunnel  of  Corti;  a,  bony  tissue  or  spiral  lamina;  b,  b, 
fibrous  tissue  covering  same  continued  as  substantia  propria  of  basilar 
membrane;  c,  c,  protoplasmic .  envelope  of  Corti's  pillars  (e,  e,);  d, 
endothelial  plates;  /,  heads  of  pillars  containing  oval  areas;  g,  head 
plates  of  pillars;  h,  hf,  inner  and  outer  hair  cells;  m,  membrana  retic- 
ularis;  k,  I,  cells  of  Hensen  and  Claudius;  n,  n,  nerve  fibers;  i,  cells  of 
Deiters  (after  Piersol). 

and  extends  to  the  free  surface  of  the  hair  cells. 
Each  cell  has  a  nucleus  near  its  middle  and  contains 
a  bright  thread-like  structure,  called  the  supporting 
fiber. 

4.  The  cells  of  Hensen  are  outer  supporting  cells  and 
consist  of  several  rows  just  outside  of  Deiters'  cells, 
where  they  form  a  well-marked  elevation  on  the  floor 
29 


45°      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

of  the  scala  media.     The  columnar  cells  just  external 
to  this  elevation  are  named  the  cells  of  Claudius. 

5.  The    lamina    reticularis    is    a    thin    cuticular 
structure  which  lies  over  Corti's  organ  and  extends 
from  the  outer  rods  as  far  as  Hensen's  cells.     This 
membrane  has  numerous  small  apertures  into  which 
the  outer  hair  cells  project. 

6.  The  membrana  lector ia  is  an  elastic  membrane 
attached  to  the  free  margin  of  the  lamina  spiralis  and 
reaching  outward  as  far  as  the  outer  row  of  hair  cells. 
This  membrane  has  no  nuclei  and  shows  fine  radial 
striations.     The  membrane  is  supposed  to  act  as  a 
damper  to  the  hair  cells. 

The  Auditory  Nerve. — The  auditory  nerve  divides 
into  two  main  parts,  the  ramus  'vestibularis  and  the 
ramus  cochlearis.  The  vestibularis  divides  into 
three  branches  which  are  the  macula  acustica,  utric- 
uli,  and  the  ampullae  of  the  inferior  and  external 
semicircular  canals.  The  ramus  cochlearis  supplies 
a  branch  to  the  macula  acustica  sacculi  and  one  to 
the  ampulla  of  the  posterior  semicircular  canal.  The 
remainder  of  the  ramus  cochlearis  is  distributed  to 
the  hair  cells  of  Corti's  organ.  Near  the  base  of  the 
osseous  spiral  lamina  there  is  situated,  in  a  special 
bony  canal,  a  ganglion  called  the  spiral  ganglion  of 
the  cochlea.  The  ganglion  cells  are  bipolar,  having 
a  dendrite  that  extends  inward  through  the  lamina 
spiralis  to  the  organ  of  Corti,  and  a  neuraxis  that 
passes  out  the  modiolus  and  thence  to  the  medulla. 
Some  of  the  dendritic  processes  pass  through  the 
tunnel  of  Corti,  so  called  tunnel  fibers,  to  reach  the 
outer  hair  cells. 


THE   ORGAN   OF   HEARING. 


451 


DEVELOPMENT  OF  THE  LABYRINTH. 
The  epithelial  lining  of  the  membranous  labyrinth 
is  derived  from  the  ectoderm  and  develops  as  a  vesic- 
ular invagination  on  each  side  of  the  epencephalon. 
After  being  constricted  off  from  the  ectoderm  this 
vesicle  develops  a  dorsomesial  evagination,  which 
gradually  grows  larger  and  becomes  the  ductus  endo- 


Fig.  310. — Three  transverse  sections  showing  development  of  otic 
vesicle  of  human  embryo  (Tourneux) :  A,  from  embryo  of  3  mm.,  showing 
auditory  pit;  B,  from  embryo  of  4  mm.,  showing  the  transformation  of 
the  pit  into  the  otic  vesicle;  C,  from  embryo  of  6  mm.,  showing  otic 
vesicle  detached  from  surface  ectoderm,  and  presenting  a  posterior 
diverticulum,  the  recessus  vestibuli. 

lymphaticus.  By  means  of  folds  and  constrictions 
the  dorsal  utriculus  and  ventral  sacculus  are  formed, 
and  also  the  semicircular  canals  which  connect  with 
the  utriculus.  The  membranous  cochlea  or  scala 
media  grows  both  in  a  longitudinal  and  a  spiral 
direction,  retaining  its  connection  with  the  sacculus 
through  the  canalis  reuniens.  This  complex  mem- 


452      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

branous  labyrinth  becomes  invested  with  developing 
bone,  and  is  filled  with  endolymph  and  surrounded 
with  perilymph.  The  developmental  history  of  the 
middle  and  external  ear  is  closely  associated  witl 
that  of  the  first  gill  cleft  of  which  they  primarilj 
form  an  associate  part. 


CHAPTER  XVI. 
OLFACTORY  ORGAN. 

The  olfactory  region  may  be  divided  into  the  vesti 
bule,  respiratory  organ;  and  the  olfactory  organ. 

1 .  The  vestibule  is  cov- 
ered with  a  continuation 
of  the  skin,  which  grad- 
ually takes  on  the  char- 
acter of  a  mucous  mem- 
brane.    The   epithelium 
is  of   a  stratified   squa- 
mous  variety,   and  pre- 
sents    hairs,     sebaceous 
glands,   and    mucous 
glands.      The    vestibule 
comprises  the  region   of 
the  anterior  nares. 

2.  The  respiratory  re- 
gion is  lined  by  ciliated 
epithelial  cells,  the  nuclei 
of  which    are  placed  at 
various    levels.      Hairs 
and  sebaceous  glands  are 
absent,  but  branched  al- 
veolar   glands    having 


Wd 


Fig.  311. — Olfactory  mucous 
membrane;  a,  sustentacular  cells; 
b,  olfactory  cells;  c,  basal  cells;  d, 
submucous  fibrous  tissue;  e,  glands 
of  Bowman;  /,  nerve  fibers  (Leroy). 


mucous  and  serous  cells 
are  present.  Numerous 
leukocytes  are  usually  found  upon  the  surface 


454     NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

3.  The  olfactory  region  is  usually  confined  to  the 
superior  turbinated  bone  and  to  the  adjacent  nasal 
septum.  In  the  fresh  condition  the  region  may  be 


Fig.  312. — Diagram  of  the  connections  of  cells  and  fibers  in  the  ol- 
factory bulb:  olf.  c,  cells  of  the  olfactory  mucous  membrane;  olf.  n, 
deepest  layer  of  the  bulb,  composed  of  the  olfactory  nerve  fibers  which 
are  prolonged  from  the  olfactory  cells;  gl,  olfactory  glomeruli,  containing 
arborization  of  the  olfactory  nerve  fibers  and  of  the  dendrons  of  the  mitral 
cells;  me,  mitral  cells;  a,  thin  axis-cylinder  process  passing  toward  the 
nerve-fiber  layer,  n.  tr,  of  the  bulb  to  become  continuous  with  fibers  of 
the  olfactory  tract;  these  axis-cylinder  processes  are  seen  to  give  off 
collaterals,  some  of  which  pass  again  into  the  deeper  layers  of  the  bulb; 
n',  a  nerve  fiber  from  the  olfactory  tract  ramifying  in  the  gray  matter  of 
the  bulb  (Schafer). 


distinguished  by  its  yellow  color,  which  is  due  to 
pigment  in  the  sustentacular  epithelial  cells. 

The  olfactory  cells  are  true  bipolar  ganglion  cells. 
The  upper  process  of  these  cells  reaches  to  the  free 


OLFACTORY   ORGAN.  455 

surface  of  the  epithelial  layer  and  is  short.  It  ter- 
minates in  six  to  eight  short  firm  hairs.  The  lower 
thinner  process  is  a  neuraxone  which  passes  through 
the  cribriform  plate  to  terminate  in  telodendria  in 
the  region  of  the  olfactory  bulb.  The  sustentacular 
cells  are  long  columnar  elements  with  oval  nuclei. 
They  give  support  to  the  ganglion  cells. 

Large  branched  tubular  glands  are  present,  called 
the  glands  of  Bowman.  They  secrete  an  albuminous 
or  serous  fluid.  Beneath  the  epithelium  there  is  a 
rich  supply  of  capillary  blood-vessels  and  lymphatics. 
Fibers  from  the  trigeminal  nerve  terminate  in  telo- 
dendria among  the  epithelial  cells  of  the  entire 
olfactory  region. 


CHAPTER   XVII. 

LABORATORY  DIRECTIONS. 

PREPARATION  OF  MATERIAL. 

I.  Spreads. — Thin   spreads  or    smears   are   made 
upon  cover  glasses  or  on  glass  slides.    The  specimens 
are  then  studied,  stained  or  unstained,  but  always 
in  some  liquid  medium.     They  may  be  fixed  and 
mounted  permanently  by  treating  the  preparations 
just  as  if  they  were  sections.     Blood,  marrow,  nerve 
cells  from  brain  or  cord,  and  scrapings  from  organs: 
as  the  liver,  may  be  prepared  in  this  way. 

II.  Teasing. — Muscle,  tendon  and  nerve  fibers  are 
easily  prepared  in  this  way.  The  teasing,  or  spread- 
ing, may  be  done  in  water  and  glycerin,  or  small 
pieces  may  be  dehydrated  with  alcohol  and  then 
teased  in  oil,  or  even  in  balsam,  thus  making  a  per- 
manent mount.     Alcohol  and  oil  harden  the  tissues, 
and  satisfactory  teasing  is  therefore  more  difficult. 

III.  Dissociation   or  Maceration   of  Tissue  Ele- 
ments— 

1.  Alcohol,  25  per  cent.;  time,  twenty-four 

or  forty-eight  hours. 

2.  Strong  acids,  as  hydrochloric  or  nitric; 

time,  twenty-four  hours. 

3.  Caustic  potash,  25  per  cent.;  time,  ten 

to  thirty  minutes. 

To  obtain  columnar  and  goblet  cells  of  the  intestine, 

456 


LABORATORY   DIRECTIONS.  457 

remove  several  inches  of  the  colon,  clean  carefully 
by  passing  water  through  it,  and  then  distend  the 
piece  with  25  per  cent,  alcohol,  ligating  both  ends. 
Next  day  open  the  bowel  and  make  light  scrapings 
from  the  mucous  surface  and  place  these  in  a  vial 
containing  equal  parts  of  alcohol  (50  per  cent.)  and 
glycerin.  Shake  the  vial  and  the  cells  will  dis- 
seminate throughout  the  fluid.  The  25  per  cent, 
alcohol  dissolves  the  cement  that  holds  these  epi- 
thelial cells  together.  If  desired,  a  little  stain  may 
be  added  to  the  glycerin  preparation. 

The  epithelium  of  the  bladder  may  be  obtained  in 
the  same  manner,  by  distending  the  organ  with  25 
per  cent,  alcohol;  also,  the  ciliated  cells  of  the 
trachea,  although  in  this  case  no  distention  is 
possible.  All  these  cells  come  away  very  easily, 
and  the  scraping  must  be  carefully  done. 

Tubules  of  the  kidney  are  readily  obtained  by 
treating  small  pieces  with  acid.  In  twenty-four 
hours,  remove  the  pieces  to  equal  parts  of  alcohol 
and  glycerin,  and  shake.  A  drop  of  this  will  show 
all  forms  of  tubules  and  glomeruli.  The  former  are 
practically  equivalent  to  epithelial  casts,  clinically 
so  important  in  urinary  analysis. 

The  caustic  potash  reaction  is  more  rapid.  Pieces 
of  tissue  may  be  treated  with  this  on  the  glass  slide 
and  examined  in  the  fluid.  Care  must  be  observed 
that  the  alkali  does  not  get  on  the  lens  of  the  micro- 
scope. 

IV.  To  Prepare  Tissue  for  Sectioning  in  Celloidin 
or  Paraffin. 

i.  Fixing    and    Hardening.  —  Fixing    consists    in 


NORMAL    HISTOLOGY   AND    ORGANOGRAPHY. 

rapidly  killing  the  cell  and  preserving  its  constitu- 
ents, nucleus  and  cytoplasm,  before  disintegration 
can  take  place.  Most  fixing  agents  coagulate  the 
protoplasm  and  cell  contents. 

(a)  Heat. — Cover-glass  preparations  may  be  fixed 
by  heating  them  in  an  oven  or  over  a  gas  flame  to 
100°  or  even  150°  C. 

(b)  Fluids. 

(1)  Acids — osmic,   i%;   chromic,  i%;   ni- 

tric, 10%;  etc. 

(2)  Salts — mercuric     chloride     saturated, 

potassium  bichromate,  3%;  etc. 

(3)  Alcohol,  95%,  or  absolute. 

(4)  Formalin,  5%. 

Acids  and  salts  may  be  used  separately  as  above, 
but  as  a  rule  different  combinations  are  used, 
formulae  of  which  are  given  on  another  page. 

(c)  Precautions. 

(1)  Fix  living  tissues,  if  possible. 

(2)  Fix  small  pieces,  so   that  fluids  may 

readily  penetrate. 

(3)  Heat  hastens  the  penetration. 

(4)  Change  as  often  as  the  fluid  becomes 

cloudy. 

(5)  Use  a  large  quanitity  of  fluid  (50  to  100 

times  the  volume  of  the  tissue) . 

2.  Washing. 

(a)  Water. — If  there  is  a  chemical  change  between 
the  fixing  agent  and  the  tissue,  use  water.  This  is 
most  frequently  the  case.  The  specimens  should  be 
very  thoroughly  washed,  preferably  in  running 
water,  for  twenty-four  hours  or  more. 

(6)  Alcohol.— When  alcohol  is  indicated,  use  the 


LABORATORY   DIRECTIONS.  459 

grades  50%,  70%,  95%,  and  leave  in  80%.  When 
ever  picric  acid  forms  a  part  of  the  fixing  agent, 
alcohol  wash  must  be  used. 

3.  Dehydrating. 

(a)  We  dehydrate  to  preserve  the  tissue  from 
action  of  bacteria. 

(6)  In  order  that  imbedding  fluids,  which  do  not 
mix  with  water,  may  penetrate  the  tissue.  Alcohol, 
the  grades  ending  with  absolute  alcohol,  is  always 
the  agent  used. 

4.  Imbedding  with  Celloidin,  Evaporation  Method. 
(a)  A  bsolute  A  Icohol  and  Ether,  Equal  Parts. — After 

thorough  dehydration  in  absolute  alcohol,  the  tissue 
is  transferred  to  absolute  alcohol  and  ether,  equal 
parts,  where  it  is  left  for  twenty-four  hours. 

(6)  Thin  celloidin,  4%,  made  by  dissolving  cel- 
loidin  shreds  in  equal  parts  of  absolute  alcohol  and 
ether.  The  tissue  may  be  left  any  length  of  time  in 
thin  celloidin,  the  longer  the  better. 

(c)  Thick  celloidin,  10%;  time,  twenty-four  hours 
or  longer. 

5.  Mounting  on  Block  and  Evaporation  of  Ether. 

(a)  Cover  surface,  of  perfectly  dry  block,  with  thin 
celloidin. 

(b)  Remove  the  tissue  from  thick  celloidin  and  place 
upon   block,    in    the   proper   position   for   cutting. 
This  is  called  orienting.     A  piece  like  a  nerve  may 
have  to  be  supported  with  needles,  and  these  re- 
moved later. 

(c)  Add  thick  celloidin,  from  time  to  time,  and  open 
any  air  bubble  that  may  appear.     Leave  the  speci- 
men in  air  until  the  ether  has  evaporated  so  that  the 


460     NORMAL   HISTOLOGY  AND    ORGANOGRAPHY. 

celloidin  does  not  feel  sticky  to  the  touch.  The 
usual  time  will  be  ten  to  twenty  minutes. 

(d)  Transfer  to  Chloroform  Vapor. — Pour  a  little 
chloroform   over  the  bottom   of  a   dish.     Set  the 
blocks  in  this  so  that  the  liquid  does  not  reach  the 
tissue.     Cover  tightly  and  leave  for  thirty  minutes. 

(e)  Transfer  to  chloroform  liquid  by  immersing  the 
tissue.     Time,  thirty  minutes. 

(/)  Transfer  to  80%  alcohol,  where  blocks  may  be 
left  permanently. 

6.  Imbedding  with  Paraffin  or  Fusion  Method. 

(a)  Intermediate  Stage. — The  tissue  is  taken  out  of 
absolute    alcohol,    where    it    has    been    thoroughly 
dehydrated,   and  is  then  treated  with  some  fluid 
that  is   miscible   on  the   one   hand   with   absolute 
alcohol,  and  on  the  other  with  paraffin.     Liquids 
used  are — 

(1)  Chloroform. 

(2)  Cedar-wood  oil. 

(3)  Turpentine. 

(4)  Xylol. 

Tissues  left  in  oils  become  brittle.  From  one  to  two 
hours  are  usually  sufficient,  depending  upon  the  size 
of  the  piece  to  be  imbedded.  Chloroform  will  harden 
the  tissue  to  a  less  degree  than  the  other  fluids. 

(b)  Melted  Paraffin. — The  melting-point  of  paraf- 
fin should  vary  according  to  the  room  temperature 
where  the  sections  will  be  cut.     The  following  table 
gives  the  relation  of  melting-point  of  paraffin  to  this 
temperature : 

Paraffin  melting- point.  Room  temperature. 

45°  C.  .  15°  to  17°  C.  or  60°  to  65°  F. 

48°  C 22°  C.  or  70°  F. 

55°  C.  .  .  24°  C.  or  75°  F. 


LABORATORY  DIRECTIONS.  461 

Tissues  are  left  in  melted  paraffin  from  two  to  six 
hours. 

(c)  Solidification  of  paraffin  may  be  accomplished 
by  means  of— 

(1)  Watch  glasses. 

(2)  Metallic  frames. 

(3)  Paper  trays. 

(4)  Tea-lead  trays. 

The  paraffin  is  poured  into  these  trays,  and  the 
tissue  quickly  transferred  to  it.  The  piece  is  then 
oriented,  and  as  soon  as  the  paraffin  has  cooled 
enough  to  form  a  crust,  the  whole  block  is  placed  in 
cold  water,  where  the  paraffin  is  quickly  cooled  so 
as  to  avoid  crystallization.  The  block  is  then  ready 
to  be  cut  in  sections. 

A.  Advantages  of  Celloidin  Imbedding. 

1 .  No  heat  is  necessary. 

2.  Large    sections    may   be    cut,    because 

penetration  is  more  complete  than 
is  the  case  with  paraffin. 

3.  Unnecessary    to    remove    celloidin    to 

stain;  sections  are  therefore  easily 
handled. 

B.  Disadvantages  of  Celloidin  Sections. 

1 .  Slow  process — at  least  three  days. 

2.  No  thin  sections. 

3.  Celloidin  may  take  the  stain,  particu- 

larly with  saffranin. 

4.  Serial  sections  difficult  to  make. 

5.  More  expensive. 


462     NORMAL   HISTOLOGY   AND    ORGANOGRAPHY. 

C.  Advantages  of  Paraffin  Imbedding. 

1.  Accommodates  very  small  objects. 

2.  Thinner  sections  may  be  cut. 

3.  Rapid  process. 

4.  Cheaper  than  celloidin  method. 

D.  Disadvantages  of  Paraffin  Imbedding. 

1.  Must  use   heat,   which   is  injurious  to 

tissues. 

2.  Must  remove  paraffin  to  stain  sections, 

and  the  latter  therefore  tear  easily. 

3.  Proper    room    temperature    necessary 

when  sections  are  cut,  in  order  to 
conform  to  melting-point  of  paraf- 
fin. 

7.  Cutting  Sections. — Use  the  whole  edge  of  the 
knife  in  cutting  celloidin  sections,   and  keep   the 
knife  wet  with  70%  alcohol.     When  cutting  paraf- 
fin sections,  the  knife  is  placed  at  right  angle  to  the 
block.     Always  trim  away  superfluous  paraffin. 

8.  Staining  celloidin  sections. 

1.  Alcohol,  95%. 

2.  Water. 

3.  Hematoxylin,  ten  minutes. 

4.  Water. 

5.  Acid  alcohol,  HC1  0.5  to  i%;  leave  the 

sections  in  this  until  all  stain  is 
washed  out  of  the  celloidin. 

6.  Water. 

7.  Eosin,    0.5%    solution,    one    to    three 

minutes. 

8.  Alcohol,  35%. 

9.  Alcohol,  95%. 


LABORATORY   DIRECTIONS.  463 

10.  Xylol  creosote  (beechwood  creosote,  20 

parts;    xylol,  80  parts). 

1 1 .  Mount  in  Canada  balsam  and  cover. 
The  sections  must  become  perfectly  transparent  in 
the  xylol  creosote.     If  they  are  cloudy  or  milky, 
water  is  present ;  and  the  sections  must  be  returned 
to  alcohol,  95%,  and  the  process  repeated.     Sections 
that  curl  should  be  flattened  out  when  lifted  out  of 
95%  alcohol,  because  in  this  the  sections  are  soft. 
In  xylol  or  in  water  the  sections  are  hard. 

9.  Staining  Paraffin  Sections. — Since  the  paraffin 
has  to  be  removed  the  sections  first  have  to  be  fixed 
to  the  glass  slide  or  cover  glass. 

(1)  Spread  fixative  on  slide.     Albumin  fixative 
consists  of  egg  albumin  and  glycerin,  equal  parts.     A 
very  thin  spread  is  all  that  is  necessary.     Schaellin- 
baum  fixative  consists  of  clove  oil  4  parts  and  thin 
celloidin  i  part.     A  thicker  spread  of  this  is  used. 

(2)  Place  section  upon  slide  and  heat  gently. 

(3)  Xylol  or  turpentine  to  remove  the  paraffin. 

(4)  Absolute  alcohol  to  remove  the  oil. 

(5)  Alcohol,  95%. 

Stain  on  the  slide,  or  immerse  the  whole  slide  in  the 
stain,  following  directions  as  for  celloidin  sections. 

Stain  in  bulk  before  imbedding  in  paraffin  when- 
ever this  is  possible,  as  then  the  sections  may 
be  mounted  from  xylol  directly  into  balsam.  An 
excellent  way  to  get  sections  smooth  is  to  float  them 
on  warm  water— not  so  warm  as  to  melt  the  paraffin 
— an4  then  lift  them  out  upon  the  glass  slide. 
Decant  surplus  water  and  put  away  for  twenty-four 
hours  to  dry.  Next  day  remove  paraffin  with  xylol 
and  stain  according  to  above  directions. 


464      NORMAIv  HISTOLOGY  AND  ORGANOGRAPHY. 

Review  of  Preparing  Tissues. 

1.  Fixing  and  hardening 

2.  Washing. 

3.  Dehydrating. 

4.  Imbedding  in  celloidin. 

5.  Mounting  on  block  and  evaporation  of 

ether. 

6.  Imbedding  in  paraffin. 

7.  Cutting  sections. 

8.  Staining  celloidin  sections. 

9.  Staining  paraffin  sections. 

The  following  is  a  brief  outline  of  the  tissues  to  be 
prepared  for  a  laboratory  course  accompanying  the 
text.  Special  technique  is  cited  whenever  indicated, 
otherwise  standard  laboratory  methods  may  be  em- 
ployed. This  outline  is  abbreviated  and  should  be 
expanded  according  to  the  skill  of  the  instructor  or 
student  and  according  to  the  laboratory  equipment. 

Mitosis. 

1 .  Growing  point  of  onion  or  lily  root  tip,  hardened 
in  Flemming  or  corrosive  sublimate,  and  cut  in  longi- 
tudinal section. 

2.  Testicle  of  grasshopper  taken  in  June,  or  ova, 
or  skin  stripped  from  tail  of  growing  tadpoles.     Iron 
nematoxylin  stain  is  excellent. 

Epithelium. 

i  Isolated  epithelial  cells  from  intestine,  trachea 
and  bladder  (see  page  457). 

2.  Epithelium  exfoliated  from  skin  of  frog  (pieces 
gathered  from  water  where  frogs  are  kept) . 

3.  Fresh  cells  scraped  from  mucous  surface  of  cheek. 

4.  Sections  of  intestine,  cornea  of  the  eye,  and  skin. 
c.  Endothelial  cells  of  mesenterv. 


LABORATORY   DIRECTIONS.  465 

Prepare  endothelium  as  follows: 

(1)  Kill  a  small  animal,  as  a  rat. 

(2)  Open  abdominal  cavity. 

(3)  Wash  out  cavity  with  sterile  water;  do  not 

handle  the  mesentery. 

(4)  Fill  cavity  with  J   per  cent,  silver  nitrate 

solution,  5  min.  See  that  mesentery  is 
bathed. 

(5)  Wash  cavity  with  J  per  cent,  nitric  acid 

solution,  5  min. 

(6)  Fill  cavity  with  alcohol  95  per  cent,  one-half 

to  one  hour,  as  convenient. 

(7)  Remove  mesentery  with  intestine  attached. 

(8)  Immerse  in  fresh  95  per  cent,  alcohol  one  to 

twelve  hours. 

(9)  Cut  intestine  away  from  mesentery  and  im- 

merse the  latter  in  fresh  95  per  cent,  alcohol, 
one-half  to  one  hour. 

(10)  Transfer  mesentery  to  clove  oil  and  expose 
to  sunlight  in  shallow  wide  dish,  three  to  five 
hours.  Direct  sunlight  is  not  good. 

(n)  Cut  mesentery  into  small  pieces  and  mount 
in  balsam.  Handle  mesentery  as  little  as 
possible  during  the  whole  process. 

Glands. 

i.  For  simple  mucous  and  serous  glands  make 
cross  sections  of  the  skin  of  a  salamander. 

Connective  Tissue. 

1.  Sections  of  young  umbilical  cord  and  of  em- 
bryos show  connective- tissue  cells. 

2.  Sections  of  fat  and  teased  fresh  pieces  of  fat. 

3.  Salamander  skin,  dehydrated  and  mounted  with 
lower  side  up  shows  connective-tissue  pigment  cells. 


466      NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

4.  Brown  connective-tissue  pigment  cells  may  be 
scraped  from  the  choroid  coat  of  the  eye  after  re- 
moving the  retina. 

5.  Sections  and  teased  preparations  of  ligamentum 
tiuchae  of  the  ox. 

6.  Sections  and  teased  preparations  of  a  tendon. 

7.  Elastic  fibers  of  the  mesentery  of  a  rat. 

PREPARATION  OF  ELASTIC  FIBERS. 

(1)  Fill  abdominal  cavity  of  a  rat  with  95  per  cent, 
alcohol,  one  hour. 

(2)  Remove   intestine   with  mesentery  attached 
and  place  in  fresh  alcohol. 

(3)  Cut  away  the  mesentery  and  mordant  with 
6  per  cent,  solution  of  boric  acid. 

(4)  Stain. 

Orcein 1  part. 

Alcohol,  95  per  cent 100  parts. 

Hydrochloric  acid 1  part 

Stain  for  one  to  twelve  hours.  The  fibers  should 
appear  dark  brown.  If  stained  too  deeply,  treat 
with  acid  alcohol,  J  per  cent,  hydrochloric  acid.  If 
too  red,  dip  the  pieces  in  fifty  per  cent,  alcohol  satu- 
rated with  ammonium  picrate. 

Cartilage. 

1 .  Cartilage  sections  may  be  cut  with  a  razor  from 
bone  joints  obtained  at  a  meat  market. 

2.  Sections  of  trachea  for  hyaline  variety.     The 
sections  must  be  cut  thin  and  not  overstained. 

Bone. 

i.  Ground  sections,  mounted  dry.  A  dry  white 
and  fat-free  bone  is  the  best.  With  a  turning  table 
ring  a  glass  slide  with  balsam.  Before  the  balsam 


LABORATORY  DIRECTIONS.  467 

sets  the  bone  may  be  mounted  dry  by  covering 
with  circular  cover  glass,  which  sticks  to  the  ring  of 
balsam. 

2.  Sections  of  decalcified  bone.  Place  a  fresh 
bone  in  95  per  cent,  alcohol  to  fix  and  harden  soft 
parts.  Next  day  begin  process  of  decalcification. 
Use  nitric  or  hydrochloric  acid,  ^  to  i  per  cent.,  using 
a  large  quantity  and  changing  fluid  twice  daily. 
Nitric  acid  may  be  used  in  i  to  10  per  cent,  strength. 
Time  required  varies  from  one  to  seven  days.  By 
means  of  sharp  needles  it  is  possible  to  determine 
when  decalcification  is  complete.  After  decalci- 
fication wash  in  running  water  for  twenty-four  hours. 

Muscle. 

1.  Smooth    muscle.     Pieces    stripped  from   the 
intestinal  wall  may  be  stained  for  twenty-four  hours 
with   dilute   hematoxylin.     Tease   in   glycerin   and 
alcohol,  or,  for  permanent  mounts,  dehydrate  and 
tease  in  oil. 

2.  Cross  sections  of  the  intestine  will  show  smooth 
muscle  in  cross  and  in  longitudinal  sections. 

3.  Heart   muscle.     Teased   specimens   and   very 
thin  sections. 

4.  Voluntary  muscle.     Sections  of  a  tongue  will 
show  fibers  both  in  cross  and  in  longitudinal  section. 

5.  Injected  muscle.     Sections  should  be  cut  very 
thick  to  show  capillaries.     Such  muscle  carefully 
teased  is  very  satisfactory. 

6.  Fresh    voluntary    fibers    may    be    teased    in 
alcohol  and  glycerin. 

Nervous  Tissue. 

i.  For  bipolar  cells  study  sections  of  the  spinal 

ganglion. 


468      NORMAL   HISTOLOGY  AND  ORG ANOGRAPHY . 

2.  For  multipolar  cells  study  sections  of  the  cere-= 
bral  cortex  and  spinal  cord  stained  with  Cox-Golgi 
method,  as  follows : 

Potassium  bichromate 20  parts. 

Corrosive  sublimate  5  per  cent. 

sol 20  parts. 

Distilled  water 40  parts. 

Potassium  chromate,  5  percent. 

sol 16  parts. 

Specimens  remain  in  this  two  weeks  or  two 
months;  after  which  wash  thoroughly  twenty-four 
hours.  Cut  sections  free-hand  as  thin  as  possible 
and  place  them  in  a  saturated  solution  of  lithium 
carbonate  for  twenty-four  hours.  Transfer  to  95 
per  cent,  alcohol,  and  then  to  clove  oil,  from  which 
they  are  mounted  in  balsam  on  a  glass  slide  and 
covered  with  a  cover  glass. 

3.  Fix  a  sciatic  nerve  with  0.5  per  cent,  osmic  acid. 
Wash  thoroughly  in  water  and  tease  either  in  glyc- 
erin or  dehydrate  and  tease  in  oil.     Study  structure 
of  medullated  fibers. 

4.  Make  cross  section  of  sciatic  nerve. 
Blood. 

1 .  Dip  a  thin  strip  of  filter  paper  in  the  blood  of  a 
frog  and  make  a  spread  either  on  a  cover  glass  or  a 
glass  slide.     Dry  in  air  and  fix  in  95  per  cent  alcohol. 
Stain  with  hematoxylin  and  eosin.     Wash  in  water 
and  dry  in  air,  after  which  the  specimen  may  be 
mounted  in  balsam. 

2.  Study   fresh   specimens   of   human   blood   for 
rouleaux  and  crenated  red  blood  corpuscles. 

3.  Thin  blood  spreads  may  be  made :    . 

(i)  On  glass  slides  by  placing  a  drop  of  blood  near 


LABORATORY   DIRECTIONS.  469 

one  end  and  with  the  end  of  a  second  slide  spread  it 
by  making  a  single  stroke  toward  the  opposite  end. 

(2)  Placing    a    small    drop    between    two    cover 
glasses  and  drawing  them  apart  in  such  a  way  that 
their  surfaces  are  always  parallel. 

(3)  Saturate  the  end  of  some  thin  blotting  paper 
and  make  a  spread  either  on  a  cover  glass  or  a  glass 
slide. 

4.  Spreads  are  dried  in  air  and    then  fixed,  by 
heat   (120°  C.),   for  two   hours,  or  equal  parts  of 
absolute  alcohol  and  ether  for   two    hours.     They 
are  then  dried  and  stained.     Wright's    stain   is   a 
short  method  and  fixes  and  stains  a  film  at  the  same 
time. 

(1)  Stain  a  blood  film   with  Wright's  fluid  one 
minute. 

(2)  Distilled  water  2  min.     Add  in  drops  upon 
cover  glass  or  slide. 

(3)  Wash  in  water  until  the  film  of  blood  becomes 
pink. 

(4)  Dry  between  filter  paper  and  mount  in  balsam. 
(For  preparation  of  Wright 's  stain  see ' l  Pathological 

Technique,"  Mallory  and  Wright,  Third  Edition.) 

5.  Blood  platelets  are  obtained  by  pricking  the 
finger  through  a  drop  of  i  per  cent,  osmie  acid. 

6.  Hemin  crystals.      Grind   together   on  a  slide 
equal  parts  of  dry  blood  and  salt.     Add  glacial  acetic 
acid  and  cover  with  cover  glass.     Heat  until  gas 
bubbles  escape.     Examine  with  high-power  of  micro- 
scope. 

Red  Marrow.— With  a  pair  of  pinchers  squeeze  a 
drop  from  the  end  of  a  rib  and  spread  on  slide  or 


470     NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

cover  glass.     Fix  and  stain  as  for  blood.     A  spread 
may  be  made  from  the  end  of  the  femur  or  any  of  the 
long  bones. 
Blood-vessels. 

1.  Sections  of  the  aorta. 

2.  Small  arteries  can  be  found  in  sections  of  the 
tongue  or  any  other  organ. 

3.  Sections  of  any  large  vein. 
Lymphatics,  Thymus  Gland,  Spleen. 

1 .  Sections  of  lymphatic  nodes. 

2.  Sections  of  thy mus  gland. 

3.  Sections  of  the  spleen. 

These  tissues  must  be  cut  thin  and  not  overstained. 
Digestive  System. 

1.  Teeth.     Ground  sections,  technique  as  for  bone. 

2.  Tongue.     Section  foliate  papillae  of  rabbit  for 
taste  buds. 

3.  Cross  section  of  esophagus. 

4.  Sections  of  cardiac  and  pyloric  end  of  stomach. 

5.  Small  intestine.     Injected  specimen  must  be 
cut  thick. 

6.  Sections  of  ileum  for  Peyer's  patches. 

7.  Large  intestine,  including  vermiform  appendix. 
Digestive  Glands. 

1.  Sections  of  parotid  and  submaxillary  gland. 

2.  Pancreas.     Injected    pancreas    for    areas    of 
Langerhans. 

3.  Liver,  including  sections  of  injected  organ  cut 
thick. 

Organs  of  Respiration. 

1 .  Sections  of  thyroid  gland. 

2.  Sections  of  trachea. 


LABORATORY   DIRECTIONS,  47! 

3.  Lung,  including  thick  sections  of  injected  organ. 
Urinary  Organs. 

1.  Suprarenal  bodies. 

2.  Kidneys.     Sections    of    injected    kidney    and 
kidney    pieces    macerated    with    hydrochloric  acid 
(see  page  457). 

3.  Sections  of  ureters. 

4.  Bladder,  preferably  sections  of  one  distended 
with  fixing  fluid. 

Reproductive  Organs. 

1.  Sections  of  testes  with  epididymis  attached. 

2.  Vas  deferens. 

3.  Sections  of  penis,  preferably  of  baby  or  a  fetus. 

4.  Prostate  gland,  preferably  an  old  one. 

5..  Ovaries.     Old  enough  to  show  corpora  lutea. 

6.  Fallopian  tubes.     Sections  of  fundus  and  isth- 
mus. 

7.  Uterus. 

8.  Placenta,  preferably  at  half  term. 

9.  Mammary  gland. 

The  Skin  and  Appendages. 

1 .  Sections  of  palm  surface  of  finger. 

2.  Sections  of  the  scalp,  tangential  and  cross. 

'3.  Nails.     Sections  of   finger  of   fetus   are  very 
good. 
Peripheral  Nerve  Endings  and  Spinal  Cord. 

1.  Sections    of    duck's    bill.     Iron    hematoxylin 
stain. 

2.  Pacinian  corpuscles  may  be  found  in  sections 
of  the  skin  of  the  finger  or  in  the  connective  tissue 
of  sections  of  the  pancreas.     They  may  be  teased 
out  from  the  mesentery. 


472      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

3.  Spinal  cord.     The  cord  of  the  horse  or  ox  is 
very  satisfactory. 
Brain. 

1.  Sections  of  cerebral  cortex. 

2.  Sections  of  cerebellar  cortex  cut  across  the 
folds. 

3.  Sections  of  closed  and  open  medulla. 

4.  Sections  of  the  pons. 

Sections  of  the  medulla  and  pons  should  be  cut 
thick  and  stained  with  Pal-Weigert  method. 
Celloidin  method  of  imbedding  is  preferable. 
The  Eye. 

1 .  Sections  of  the  whole  eye  imbedded  in  celloidin, 

2.  Sections  of  the  cornea. 

3.  Sections  of  the  retina. 

4.  Sections  of  the  eyelid. 
The  Internal  Ear. 

Sections  of  the  cochlea  must  be  decalcified. 
Cochlea  of  a  young  kitten  is  very  satisfactory. 

STANDARD  FIXING  SOLUTIONS. 
Carney's  Acetic-alcohol  Mixture. 

Glacial  acetic  acid 1  part. 

Absolute  alcohol 3  parts. 

Pieces  one  centimeter  thick  are  fixed  in  one-half  to 
one  hour.  The  after-treatment  is  with  absolute 
alcohol. 

Osmic  Acid. — One-half  to  one  per  cent,  aqueous 
solution. 

Fix  for  three  to  twenty-four  hours  and  then  wash 
thoroughly  in  running  water. 


LABORATORY   DIRECTIONS.  473 

Flemming's  Solution. 

Osmic  acid,  1  per  cent,  aqueous 

solution 10  parts. 

Chromic  acid,  1  per  cent,  aque- 
ous solution 25  parts. 

Glacial  acetic  acid,  1  per  cent. 

aqueous  solution 10  parts. 

Distilled  water 55  parts. 

Fix  for  twenty-four  hours  or  more  and  wash  thor- 
oughly in  running  water. 

Flemming's  Strong  Solution. 

Osmic  acid,  2  per  cent,  aqueous 

solution 4  parts. 

Chromic  acid,  1  per  cent,  aque- 
ous solution 15  parts. 

Glacial  acetic  acid 1  part. 

This  is  a  good  fixing  agent  for  nuclear  structures 
and  therefore  for  mitosis. 

Corrosive  Sublimate. 

Saturated  solution  in  distilled  water.  Fix  for 
twenty-four  hours  or  more  and  wash  in  running  water. 
After  twenty-four  hours,  transfer  to  70  per  cent, 
alcohol  to  which  a  few  drops  of  iodin  and  potassium 
iodid  have  been  added.  The  iodin  removes  any 
crystals  of  sublimate  that  may  have  formed. 

Picric  Acid. 

Saturated  aqueous  solution.  Fix  for  twenty-four 
hours,  or  longer,  after  which  wash  in  70  per  cent, 
alcohol. 

Picrosulphuric  Acid. 

Picric  acid,  saturated  aqueous 

solution 100  parts. 

Sulphuric  acid,  concentrated...      1  part. 

Distilled  water 200  parts. 

After-treatment  same  as  for  picric  acid. 
Nitric  Acid.— Aqueous  solution,  3  to  10  per  cent. 


474      NORMAL   HISTOLOGY   AND   ORGANOGRAPHY. 

Fix  for  several  hours  and  wash  thoroughly  in  running 
water. 

Chromic  Acid. — Aqueous  solution  J  to  i  per  cent. 
Small  pieces  are  fixed  for  twenty-four  hours.  Wash 
in  running  water  and  pass  through  the  ascending 
grades  of  alcohol,  preferably  in  the  dark. 

Miiller's  Fluid 

Potassium  bichromate 2.5  gm. 

Sodium  sulphate 1.0  gm. 

Water 100  c.c. 

Fix  for  several  weeks,  preferably  in  the  dark.  At 
first  the  fluid  should  be  changed  daily.  Wash  in 
running  water  for  twenty-four  hours  and  place 
directly  in  70  per  cent,  alcohol.  Dehydrate  prefer- 
ably in  the  dark. 

Zenker's  Fluid. 

Potassium  bichromate 2.5  gm. 

Sodium  sulphate i.o  gm. 

Corrosive  sublimate 5.0  gm. 

Glacial  acetic  acid 5.0  gm. 

Water 100  gm. 

It  is  better  to  add  the  acetic  acid  just  before  us'mg 
and  not  to  add  it  to  the  stock  solution.  Fix  tissues 
in  this  fluid  for  six  to  twenty-four  hours.  Wash  in 
running  water  twenty-four  hours  and  transfer  to 
alcohol,  using  the  grades.  Sublimate  crystals  are 
removed  by  iodized  alcohol  as  with  corrosive  subli- 
mate solutions. 
Formalin. 

Formalin  (40  per  cent.  Formal- 
dehyde)   5  to  10  parts. 

Water 90  parts. 

Small  pieces  are  fixed  in  twelve  to  twenty-four  hours. 
As  sections  do  not  stain  well  after  this  fixation,  it 


LABORATORY   DIRECTIONS.  475 

is  better  to  transfer  the  pieces  to  some  standard  salt 
solution  and  then  wash  and  dehydrate. 

Potassium  Bichromate  and  Formalin. 

Potassium    bichromate   2    per 

cent,  aqueous  solution 90  parts. 

Formalin 10  parts. 

Fix  for  several  days  or  weeks.  Wash  in  running 
water  and  dehydrate  with  alcohol.  This  is  a  good 
fixation  for  the  central  nervous  system. 

STANDARD  STAINS. 
Aqueous  Borax-carmin  Solution. 

Borax 8  gm. 

Carmin 2  gm. 

Water 150  c.c. 

Grind  together  the  borax  and  carmin.  Add  the 
water  and  in  twenty-four  hours  filter.  Stain  sections 
for  twelve  hours  or  longer.  Treat  with  acid-alcohol 
as  necessary. 

Alcohol  Borax-carmin  Solution. 

Carmin 3  gm. 

Borax 4  gm. 

Water 93  c.c. 

Alcohol,  70  per  cent 100  c.c. 

Filter  and  stain  as  for  the  aqueous  solution. 
Cochineal  Solution. 

Cochineal,  powdered 7  gm. 

Alum,  roasted 7  gm. 

Water 100  c.c. 

Boil  down  to  one-half  its  volume,  stirring  freely. 
When  cool  filter  and  add  a  few  drops  of  carbolic  acid. 
This  fluid  does  not  overstain  and  acts  rapidly.  After 
staining  wash  in  distilled  water,  as  alcohol  precipi- 
tates the  alum. 


476     NORMAL  HISTOLOGY  AND  ORGANOGRAPHY. 

Alum-carmin  (Grenacher). 

Alum   solution,  3  per  cent,  to   5 

per  cent 100  c.c. 

Carmin 1  to  5  gm. 

Boil  for  fifteen  minutes,  cool  and  filter.  Add  enough 
water  to  replace  that  lost  by  boiling.  Wash  the 
sections  in  water  after  staining. 

Bohmer's  Hematoxylin. 

Hematoxylin 1  gm. 

Alcohol,  absolute 10  c.c. 

Potassium  alum 10  c.c. 

Distilled  water 200  c.c. 

Dissolve  the  hematoxylin  in  alcohol  and  the  alum  in 
water.  Add  the  first  to  the  second  solution  while 
continually  stirring.  Allow  this  preparation  to 
stand  in  an  open  jar  for  two  weeks,  to  ripen,  when 
the  color  will  change  from  violet  to 'blue.  After 
filtering  the  stain  is  ready. 

Delafield's  Hematoxylin. 

Hematoxylin  crystals 4  gm. 

Absolute  alcohol 25  c.c. 

Ammonium  alum,  sat.  aq.  sol.  .400  c.c. 

Alcohol  95  per  cent 100  c.c. 

Glycerin 100  c.c. 

Dissolve  the  hematoxylin  in  absolute  alcohol  and  add 
the  alum  solution.  Place  in  open  vessel  for  four 
days,  filter,  and  add  the  95  per  cent,  alcohol  and 
glycerin.  In  a  few  days  filter  again. 

Ehrlich's  Hematoxylin. 

Hematoxylin  crystals 2  gm. 

Absolute  alcohol 60  c.c. 

Glycerin  )  saturated  with  60  c.c. 

Distilled  water  f  ammonia-alum   60  c.c. 

Glacial  acetic  acid 3  c.c. 

Expose  to  light  for  a  long  time.  It  is  ready  for  use 
when  it  acquires  a  deep  red  color. 


LABORATORY   DIRECTIONS.  477 

Heidenhain's  Iron  Hematoxylin. 

Sections  that  have  been  fixed  in  sublimate  solu- 
tions are  placed  in  a  2.5  per  cent,  aqueous 
solution  of  ammonium  sulphate  of  iron  for  four  to 
eight  hours.  Rinse  thoroughly  in  water  and  place 
in  a  hematoxylin  solution  prepared  as  follows : 

Hematoxylin  crystals 1  gm. 

Absolute  alcohol 10  c.c. 

Distilled  water 90  c.c. 

Dissolve  the  hematoxylin  in  the  alcohol  and  add  the 
water.  This  solution  should  stand  in  an  open  vessel 
for  four  weeks,  and  before  using  should  be  diluted 
with  an  equal  volume  of  distilled  water. 

Stain,  the  above  sections  twelve  to  twenty-four 
hours,  rinse  in  tap  water  and  return  to  ammonium 
sulphate  of  iron  solution  until  black  clouds  cease  to 
be  given  off  from  the  sections.  Rinse  in  distilled 
water,  dehydrate,  and  mount  in  balsam. 

This  is  a  good  stain  for  mitosis. 

Anilin  Stains. 

These  are  basic  or  acid  stains.  The  basic  stains 
are  safranin,  methylene-blue,  methyl  green,  gentian 
violet,  methyl  violet,  Bismarck  brown,  thionin,  and 
tolUidin  blue,  and  stain  nuclei.  The  acid  stains  are 
eosin,  erythrosin,  acid  fuchsin,  orange  G.  and  nigro- 
sin,  and  stain  cytoplasm. 

These  stains  are  used  in  water  solutions  and  of 
\  to  i  per  cent,  strength,  to  which  a  little  alcohol 
may  be  added. 

Pal-Weigert  Method  of  Staining  Sections  of  Brain 
or  Cord. 

Mordant  celloidin  sections  for  twenty-four  hours 


478      NORMAL  HISTOLOGY   AND   ORGANOGRAPHY. 

in  3  to  5  per  cent,  aqueous  solution  of  potassium 
bichromate.  Wash  in  water  and  transfer  to  the 
following  stain : 

Hematoxylin  crystals 1  gm. 

Alcohol  95  per  cent 10  c.c. 

Lithium  carbonate,  sat.  aq.  sol.   1  c.c. 
Water 90  c.c. 

Dissolve  the  hematoxylin  in  alcohol  first,  and  then 
add  the  balance  at  the  time  of  using.  Stain  the 
sections  in  this  for  twenty-four  hours.  Wash  in 
water  and  transfer  to  a  0.25  per  cent,  fresh  solution 
of  potassium  permanganate  for  one-half  to  two  min- 
utes. Wash  freely  in  water  and  place  in  the  follow- 
ing Pal  solution : 

Oxalic  acid 1  gm. 

Potassium  sulphate 1  gm, 

Water 200  c.c. 

This  will  differentiate  the  gray  and  white  matter 
in  one  to  three  minutes.  The  nerve  fibers  should 
stain  blue.  If  the  sections  are  too  dark  they  may 
be  carried  through  the  permanganate  and  Pal's  so- 
lution a  second  time.  Transfer  to  water  for  several 
hours,  dehydrate,  and  mount  in  balsam. 

For  a  more  complete  description  of  laboratory 
methods,  including  injections,  fixing  of  tissues,  and 
special  staining  methods,  see  the  following  texts: 

"Pathological  Technique/'  Mallory  and  Wright, 
Third  Edition. 

"  Microtomist's  Vademecum,"  Lee. 

Bohm-Davidoff-Huber,  "Histology,"  Second  Edi- 
tion, 1904. 


INDEX 


ABOMASUM,  192 

Accessory  chromosome,  283 

thyroid  glands,  211 
Accommodation,  muscles  of,  420 
Acetic-alcohol,  Carney's,  472 
Achromatin,  38 
Acid,  chromic,  474 

nitric,  473 

osmic,  472 

picric,  473 

picrosulphuric,  473 
Acini,  214 

Acrodont  dentition,  169 
Adenoids,  180 
Adventitia  of  blood-vessels,  109, 

in 

Agminated  lymph-nodules,  198 
Air  cells  of  lung,  244 

sacs  of  lung,  244 
Alimentary  canal,  classification, 

136 

lymphatics  of,  205 
nerve-supply  of,  206 
Alum  carmin,  476 
Alveoli  of  lung,  245 
Amitosis,  44 
Amphipyrenin,  38 
Ampullae  of  Thoma  of  spleen,  133 
Anaphase,  43 
Anilin  stains,  477 
Anisotropic  muscle,  90 
Anterior    gray    commissure    of 
cord,  375 

ground  bundle,  383 

horn  of  cord,  376 
Appendices  epiploicae,  201 
Aqueous  humor,  428 
Arachnoid  of  brain,  386 

of  cord,  373 

^.rbor  vitae  of  cerebellum,  398 
,  mandibular,  138 

\maxillary,  139 


Archenteron,  30 
Arcuate  fibers,  390-392 

nucleus,  391,  393 
Area  acusticae,  388 
Areas  of  lyangerhans,  62 
Areolar  connective  tissue,  72 
Arrector  pili,  348 
Arteries,  109 

helicine,  291 
Arteriosclerosis,  123 
Asthma,  243 
Atheroma,  123 
Atria  of  lung,  244 
Attraction  sphere,  37 
Auditory  meatus,  437 

nerve,  450 

Auerbach's  plexus,  190,  206 
Axis  cylinder  of  nervous  tissue, 

95,  99 


BARTHOUN'S  glands,  300 
Bertini's  columns,  261 
Bile  duct,  220,  222 
Bipolar  nerve  cells,  97 
Bladder,  271 

mucous  membrane  of,  272 

trigone  of,  272 

vessels  and  nerves  of,  274 
Blastophore,  30 
Blood,  116 

crenated  red  blood-corpuscles, 
117 

ghost  corpuscles,  116 

hemin  crystals,  120 

hemoglobin,  116 

platelets,  119 

red  blood-corpuscles,  116 

rouleaux,  116 

stroma,  116 

white  blood-corpuscles,  118 
Blood-poisoning,  134 

479 


480 


INDEX 


Blood-supply  of  bone,  80 

of  brain,  405 

of  large  intestine,  203 

of  lungs,  248 

of  muscle,  92 

of  small  intestine,  203 

of  spinal  cord,  409 

of  stomach,  203 

of  teeth,  1 66 

of  tongue,  1 80 
Blood-vessels,  109 

adventitia  of,  109,  in 

arteries,  109 

capillaries,  115 

general  considerations,  123 

intima,  109 

media,  no 

of  central  nervous  system,  409 

of  eye,  430 

of  kidney,  266 

of  suprarenal  bodies,  255 

stigmata  and  stomata,  116 

vasa  vasorum,  112,  124 
Body  cavity,  32 
Bone,  66,  81 

blood-supply  of,  80 

canaliculi,  78 

cancellate,  80 

development  of,  81 

diploe,  80 

endochondral,  81 

general  considerations,  84 

Haversian  system,  78 

intramembranous,  81 

lacunae,  77 

ossification  of,  83 

osteogenetic  layer,  80 

primary  areolae  of  Sharpey,  81 

regeneration  of,  83 

secondary  areolae  of  Sharpey, 
82 

Sharpey's  fibers,  80 

Volkmann's  canals,  80 
Bones  of  ear,  439 
Borax  carmin,  475 
Bowman's  capsule  of  kidney,  262 

glands,  455 
Brain,  384 

arachnoid  of,  386 

blood-supply  of,  409 

development  of,  33,  384 

divisions  of,  384 


Brain,  dura  of,  385 

meninges  of,  385 
-  pia  of,  385 
Bronchi,  240 

eparterial,  250 

hyparterial,  250 

respiratory,  244 
Briinner's  glands,  199 
Burdach's  columns,  379,  380,  387, 

390 


CALAMUS  scriptorius,  378 
Canal  of  Petit,  430 

of  Schlemm,  415 
Canaliculi,  bone,  78 
Cancellate  bone,  80 
Capillaries,  115 

lymphatic,  125 
Capsule,  lens,  428 

of  Glisson,  218,  221 

of  kidney,  Bowman's,  262 

Tenon's,  415 
Carbon,  19 
Cardiac  muscle,  87 
Carmin,  alum,  476 

borax,  475 

Carney's  acetic-alcohol,  472 
Cartilage,  66,  74 

elastic,  76 

general  considerations,  77 

hyaline,  75 

lacunae  of,  73,  75 

of  trachea,  240 

white  fibrous,  76 
Cartilages  of  larynx,  231 
Casts  of  kidney,  tubular,  265 
Cauda  equina,  371 
Cell,  23,  25 

air,  of  lung,  244 

cleavage  of,  laws  of,  44 

column,     Waldeyer's    central, 
376 

cortical,  399 

decidual,  327 

defined,  26,  35 

Deiters'  supporting,  449 

endothelial,  of  artery,  109 

fat,  55 

general  considerations,  45 

giant,  122 

goblet,  58 


IND^X 


481 


Cell,  inclusions  of,  39 

interstitial,  of  testis,  62 

mast,  119 

membrane  of,  39 

mossy,  104 

multipolar,  98 

nerve,  bipolar,  97 

of  posterior  horn,  375 

unipolar,  96 

of  connective  tissue,  66 

of  Hansen,  445 

of  liver,  227 

of  marrow,  122 

parietal,  of  salivary  glands,  210 

pigment,  67 

plasma,  69 

polymorphic,  of  cerebrum,  405 

polynuclear,  119 

prickle,  341 

Purkinje's,  400 

pyramidal,  of  cerebrum,  405 

spider,  104 

stellate,  of  cerebellum,  399 
of  Kupffer,  229 

tactile,  365 

theory,  34 

wandering,  69,  119 
Celloidin  imbedding,  459 
advantages  of,  461 
disadvantages  of,  461 

sections,  staining  of,  462 
Cementoblasts,  163,  164 
Cementum,  159 
Centro-acinal   cells   of   pancreas, 

214,  215 

Centrosomes,  37 
Cerebellar  tract,  direct,  380 
Cerebellum,  398 

arbor  vitae  of,  399 

climbing  fibers  of,  401 

cortical  cells,  399 

granular  layer,  401 

inferior  peduncle  of,  388 

medullary  substance,  401 

mossy  fibers,  401 

Purkinje's  cells,  400 

stellate  cells,  399 
Cerebrospinal  system,  104,  105 
Cerebrum,  403 

fibers  of,  405 

medullary  substance,  406 

molecular  layer,  403 


Cerebrum,  polymorphic  cells,  405 

pyramidal  cells  of,  405 
Ceruminous  glands,  437 
Cervical    enlargement   of   spinal 

cord,  371 
Chondrin,  73 
Chorion,  328 
Chorionic  villi,  329 
Choroid  coat,  418 

fissure,  411 
Chroma  tin,  38,  41 
Chromic  acid,  474 
Chromosomes,  28,  42 

accessory,  283 

daughter,  42 

in  mitosis,  40 
.     synapsis  of,  281 
Ciliary  body,  420 

muscles,  420 

processes,  420 
Circulatory  endocardium,  108 

epicardium,  108 

heart,  108 

myocardium,  108 

system,  108 
Circumvallate  papillae  of  tongue, 

176 

Clarke's  column,  376,  380 
Clava,  388 
Cleavage,  28 

of  cells,  laws  of,  44 
Cleft  palate,  142 
Climbing  fibers  of  cerebellum,  401 
Cochineal  solution,  475 
Cochlea,  440,  443 
Coelenteron,  30 
Cohnheim's  fields,  89 
Collaterals,  95 
Colostrum,  334 
Column  of  Bertini,  261 

of  Burdach,  379,  380,  387,  389 

of  Clarke,  376,  380 

of  Goll,  379,  380,  387,  389 

of  Sartoli,  277 
Comma  tract,  379,  380 
Commissure,    posterior   gray,   of 

cord,  375 

Cone,  implantation,  101 
Conjunctiva,  433,  434 
Connective  tissue,  66 
areolar,  72 
cells  of,  66 


482 


INDEX 


Connective  tissue,  classification, 

TO 

embryonic,  66 
diagnostic  points  of,  73 
fibers  of,  70 

general  considerations,  72 
products  of,  69 
reticular,  71 
white  fibrous,  70 
yellow  elastic,  71 
Corium,  341 
Cornea,  415 
Corneum,  339 
Corona  radiata,  308 
Coronary  cushion,  354 
Corpora  cavernosa,  289     • 

structure  of,  290 
lutea,  62,  313 
Corpus  spongiosum,  289 

structure  of,  292 
Corpuscles,  genital,  367 
ghost,  116 
Grandry's,  365 
Malpighian,  262 
of  kidney,  262 
of  spleen,  132 
Meissner's,  366 
of  Hassal,  130 
of  Herbst,  366 
of  Highmore,  276 
Pacinian,  369 
red  blood-,  116 

crenated,  117 
white  blood,  1 1 8 
Corrosive  sublimate,  473 
Cortex  of  kidney,  261 
Cortical  cells,  399 
Corti's  organ,  447 

rods,  448 

Cowper's  glands,  297 
Cremasteric  fascia,  275 
Crenated'   red    blood-corpuscles, 

117 

Crescents  of  Gianuzzi,  210 
Cretinism,  237 
Crossed  pyramidal  tract,  381 
Crura  cerebri,  395 
Crypts  of  Lieberkiihn,  197 

of  stomach,  186 
Crystals,  hemin,  120 
Cushion,  coronary,  354 
Cuticle,  50 


Cutis  vera,  341 
Cutting  sections,  462 
Cystic  duct,  220,  222,  223 
Cysts,  sebaceous,  359 
Cytogenic  glands,  58,  62 
Cytolymph,  36,  39 
Cytoplasm,  36,  39 
Czermak's   interglobular   spaces, 


DANDRUFF,  359 

Dartos,  275 

Daughter  chromosomes,  42 

skein,  43 

star,  43 
Deciduae,  325 
Decidual  cells,  327 
Decussation,  motor,  318,  389 

sensory,  390 
Dehiscent  glands,  58,  62 
Dehydrating,  459 
Deiters'  nucleus,  382 

supporting  cells,  449 
Demilunes  of  Heidenjiain,  210 
Dendrite,  96 
Den  tin,  155 

secondary,  157 
Dentition,  143 

acrodont,  169 

pleurodont,  169 

thecodont,  169 
Dermis,  341 

Descemet's  membrane,  416,  417 
Determination  of  sex,  283 

influences  affecting,  284 
Deutoplasm,  309 
Development,  general,  23 

of  bone,  81 

of  brain,  33,  384 

of  teeth,  170 
Diad,  282 
Diaster,  43 
Digestive  glands,  207 
Diploe,  80 
Direct  cerebellar  tract,  380 

pyramidal  tract,  383 
Discus  proligerus,  306 
Dissociation  of  tissue  elements, 

456 

Diverticulum,  Meckel's,  194 
Doyer's  elevation,  361 


INDEX 


483 


Duct,  Hensen's,  443 

hepatic,  222 

lactiferous,  333 

of  Santorini,  214 

of  Wirsung,  213 
Ductless  glands,  62 
Ductus  endolymphaticus,  441 

reuniens  of  Hensen,  446 
Dura  of  brain,  385 

of  cord,  372 


EAR,  bones  of,  439 

external,  437 

internal,  440 

labyrinth  of,  440 

middle,  438 
Ectoderm,  30 
Ectosarc,  37 
Ejaculatory  duct,  286 
Elastic  cartilage,  76 
Eleidin,  340 
Embryology,  23 

Embryonic  connective  tissue,  66 
Enamel,  147 

rods,  directions  of,  150 
Encephalon,  344 
Endocardium,  circulatory,  108 
Endochondral  bone,  81 
Endolymphatic  duct,  441 
Endometrium,  321 
Endomysium,  88 
Endoneurium,  104 
Endosarc,  37 
Endothelial  cells  of  artery,  109 

layer  of  artery,  109 
Endothelioma,  63 
Endothelium,  62 
End-plate  muscle,  361 
Enlargement,   lumbar,   of  spinal 

cord,  371 
Entoderm,  30 
Environment,  25 
Eosinophiles,  119,  122 
Eparterial  bronchus,  250 
Epicardium,  circulatory,  108 
Epidermis,  339 
Epididymis,  286,  287 
Epidural  space,  373 
Epimysium,  88 
Epineurium,  104 
Epithelial  glands,  57 


Epithelial    glands,    classification 

of,  6 1 

Epithelioma,  63 
Epithelium,  43,  52,  54 

germinal,  356 
Epoophoron,  317 
Erythrocytes,  116 
Esophagus,  182 
Eustachian  tube,  439 
Excretory  ducts  of  testicle,  284 
Exolemma,  101 
Exophthalmic  goiter,  237 
External  ear,  437 
Eyes,  411 

blood-vessels  of,  430 

coats  of,  413 

refractory  media  of,  428 

tunica  externa  of,  414 


FALLOPIAN  tubes,  313 
development  of,  316 
structure  of,  315 
Falx  cerebelli,  385 

cerebri,  385 
Fascia,  cremasteric,  275 

infundibuliform,  275 

intercolumnar,  275 
Fasciculi  of  muscle,  88 
Fasciculus  solitarius,  388 

teres,  393 
Fat  cells,  55 
Fauces,  137 
Fenestra  ovales,  441 

rotunda,  445 
Fenestrated  membrane  of  Henle, 

109,  no 

Ferrein's  pyramids,  261 
Fertilization,  27 
Fibers,  arcuate,  390-392 

climbing,  of  cerebellum,  401 

medullated  nerve,  99 

mossy,  401 

nerve,  99 

non-medullary,  103 

of  cerebrum,  405 

of  connective  tissue,  69 

posterior  root  of,  termination, 
380 

Sharpey's,  80 
Fibrillar  mass,  36 
Fibrils  of  nervous  tissue,  103,  104 


484 


INDEX 


Fibroblast,  163,  164 

Fibroma,  72 

Filiform  papillae  of  tongue,  175 

Fillet,  397 

Filum  terminale,  371 

Fissure,  choroid,  411 

Fissures  of  liver,  217 
of  spinal  cord,  373 

Fixing  and  hardening  tissues,  457 

Flemming's  solution,  473 

Fluid,  Miiller's,  474. 

Foliate  papillae  of  tongue,  179 

Follicle,  Graafian,  304,  305 

Follicles  of  hair,  345 

Follicular  fluid,  306 
glands,  62 

Food,  influence  of,  on  sex  deter- 
mination, 284 

Foramen  cecum  of  medulla,  389 

of  tongue,  174 
of  Winslow,  219 

Formalin,  474 

potassium  bichromate  and,  475 

Formatio    reticularis,    391,    393, 

397 

Fovea  centralis,  426 
Free  sensory  nerve  endings,  364 
Frenum,  lingual,  174 
Frog,  351 
Fungiform    papillae    of    tongue, 

i75»  176 
Funiculus  cuneatus,  387,  390 

gracilis,  387,  390 

of  nervous  tissue,  104 


GALL-BLADDER,  222 
Ganglia,  96 
Ganglion,  spinal,  97 

spiral,  450 

Gastric  glands,  187,  188 
Gastrula  stage,  29 
Gelatinosa   substantia   Rolando, 

375 

Genital  corpuscles,  367 
Germ  layer,  derivatives  of,  33 
Germinal  epithelium,  356 

spot,  310 

vesicle,  309 
Ghost  corpuscles,  116 
Giant  cells,  122 
Gianuzzi's  crescents,  210 


Glands,  cytogenic,  58,  62 

defined,  57 

dehiscent,  58,  62 

ductless,  62 

epithelial,  57 

classification  of,  61 

follicular,  62 

hemolymph,  129 

lymph,  57,  62,  127 

of  Bartholin,  301 

of  Bowman,  455 

of  Littre,  297 

of  Moll,  433 

of  Montgomery,  335 

of  penis,  289,  290,  292 

of  Tyson,  290 

suprarenal,  62,  253 

thyroid,  62 

unicellular,  57,  62 
Glisson's  capsule,  218,  221 
Globus  major,  285 

minor,  285 
Glottis,  235 
Goblet  cells,  58 
Goiter,  237 

exophthalmic,  237 
Goll's  column,  379,  380,  387   390 
Gower's  tract,  380 
Graafian  follicle,  304,  305 
follicular  fluid,  306 
stratum  granulosum,  306 
theca,  306 

Grandry's  corpuscle,  365 
Granular  layer,  Tomes',  156 
Granules,  zymogen,  of  pancreas, 

218 

Gray   commissure  of  cord,   pos- 
terior, 375 

matter  of  pons,  396 

of  spinal  cord,  375 
Ground  bundle,  anterior,  383 


HAIR,  343 

follicles  of,  345 

papillae  of,  348 
Hairs,  tactile,  346 
Hansen's  cells,  449 
Hardening  tissues,  457 
Harelip,  141 
Hassal's  corpuscles,  130 
Haversian  system  of  bone,  78 


INDEX 


485 


Heart,  circulatory,  108 
Heidenhain's  demilunes,  210 
Helicine  arteries,  291 
Hematoblasts,  122 
Hematoxylin,  476 
Hemiii  crystals,  120 
Hemoglobin,  116 
Hemolymph  glands,  129 
Hemolysis,  124 

Henle's    fenestrated    membrane, 
109,  no 

layer,  346,  347 
Hensen's  duct,  443 

ductus  reuniens,  446 

median,  disc,  90,  91 
Hepatic  cords,  226 

duct,  222 

Herbst's  corpuscles,  366 
Heredity,  24,  47,  48 
Highmore's  corpuscles,  276 
Hilus  of  kidney,  259 
Histology,  23 
Hoof  horn,  354 

matrix,  354 

of  horse,  351 

tubes,  354 
Horny  laminae,  351 
Humor,  aqueous,  428 

vitreous,  412,  430 
Huxley's  layer,  344,  347 
Hyaline  cartilage,  75 
Hyaloid  membrane,  430 
Hyaloplasm,  36,  39 
Hydatid  of  Morgagni,  287 
Hydrogen,  19 
Hyparterial  bronchi,  250 
Hypoderm,  30 
Hypophysis  cerebri,  62 


IMBEDDING,  459 
celloidin,  459 

advantages  of,  461 
disadvantages  of,  461 
paraffin,  460 

advantages  of,  462 
disadvantages  of,  462 
Implantation  cone,  101 
Inferior  peduncle  of  cerebellum, 

388 

Infundibuliform  fascia,  275 
Infundibulum  of  lung,  247 


Insensitive  lamina,  351 
Intercellular  bridges,  49 

spaces,  49 

Intercolumnar  fascia,  275 
Interglobular  spaces  of  Czermak, 

156 

Internal  ear,  440 
Interstitial  cells  of  testis,  62 

elements  of  testes,  278,  279 
Intestine,  large,  200 

blood-supply  of,  203 

coats  of,  20 1 

sacculae  of,  200,  201 
small,  194 

blood-supply  of,  203 

mucosa,  194 

muscular  layer,  200 

serosa,  200 

submucosa,  199 

villi  of,  196 

Intima  of  blood-vessels,  109 
Intramembraneous  bone,  81 
Involuntary     muscle,     distribu- 
tion of,  86 
Iridica  retinas,  428 
Iris,  420 
Isotropic  muscle,  90 


JAUNDICE,  222 

Jelly,  Wharton's,  67,  331 


KARYOKINESIS,  40 
Karyolymph,  38 
Karyoplasm,  39 
Keraphyllous  tissue,  351 
Keratin  granules,  354 
Keratohyalin,  340 
Kidney,  257 

blood-vessels  of,  266 

Bowman's  capsule  of,  262 

cortex  of,  260 

development  of,  259 

hilus  of,  259 

labyrinth  of,  261 

Malpighian  corpuscle  of,  262 

medulla  of,  260 

medullary  rays  of,  261 

nerves  of,  269 

pelvis  of,  260 

renal  sinus,  278 


486 


INDEX 


Kidney,  structure  of,  259 

tubules  of,  262 
Knots,  nuclear  net,  40 
Krause's  membrane,  90 
Kupffer's  stellate  cells,  229 


LABORATORY  directions,  450 
Labyrinth  of  internal  ear,  440 

of  kidney,  261 
Lacrimal  apparatus,  435 

groove,  141 
Lacteals,  196 
Lactiferous  duct,  331 
Lacunae,  bone,  77 

of  cartilage,  73,  75 
Lamellae,  352 
Lamina  choroidea,  415 

cribrosa,  414,  427 

fusca,  415 

homy,  351 

reticularis,  450 

insensitive,  351,  353 

spiralis,  444 

sensitive,  351,  353 

vascular,  351,  353 
Laminitis,  355 

Langerhans,  areas  of,  62,  215 
Lantermann-Schmidt    segments, 

103 
Large  intestine,  200 

blood-supply  of,  203 
coats  of,  201 
sacculae  of,  200,  201 
Larynx,  231 

cartilages  of,  231 

mucous  membrane  of,  233 
Lateral  horn  of  cord,  376 
Laws  of  cell  cleavage,  44 
Layer,    endothelial,     of     artery, 
109 

Henle's,  346,  347 

Huxley's,  346,  347 

Malpighian,  341 

Tomes'  granular,  156 

Weil's,  159 
Lemniscus,  397 
Lens,  411,  428,  429 

capsule,  428 
Leucocytes,  118 

large  mononucleated,  119 
Lieberkiihn's  crypts,  197 


Ligaments  of  liver,  217 
Ligamentum      spirale      cochleae, 

.443 

Lingual  frenum,  174 
Lingula,  391 
Linin,  38 
Lipoma,  69 

Lissauer's  marginal  ground  bun- 
dle, 379 

Littre's  glands,  297 
Liver,  216 

blood-supply  of,  219 

cells  of,  227 

fissures  of,  217 

function  of,  227 

ligaments  of,  217 

lobes  of,  217 

lobules  of,  218 

lymphatics  of,  229 

nerves  of,  229 
LO  wen  thai' s  tract,  382 
Lumbar    enlargement    of    spinal 

cord,  371 
Lungs,  242 

air  cells  of,  244 
sacs  of,  244 

alveoli  of,  245 

atria  of,  244 

blood-supply  of,  248 

infundibulum  of,  247 

lobules  of,  245 

lymphatics  of,  251 

nerves  of,  252 

respiratory  bronchi,  244 

structure  of,  244,  247 
Lunula,  350,  351 
Lygoeus  bicrucis,  47 
Lymph  duct,  thoracic,  126 

glands,  57,  62,  127 

node,  agminated,  198 
function  of,  133 
solitary,  128 
Lymphatic  capillaries,  125 

vessels,  125 

Lymphatics  of  alimentary  canal, 
205 

of  liver,  229 

of  lungs,  251 

of  mammary  glands,  336 

of  testicle  289 
Lymphocytes,  119 
Lymphoglandulae,  57,  62 


INDEX 


487 


MACULA  acustica  sacculi,  442 
utriculi,  442 

lutea,  426 
Malpighian  corpuscle  of  kidney, 

262 
of  spleen,  132 

layer,  346 

pyramids,  260 
Mammary  glands,  332 
lymphatics  of,  336 
nerves  of,  335 
vessels  of,  335 
Mandibular  arch,  138 
Marrow,  121 

cells  of,  122 

myelocytes,  122 
Masculine  uterus,  293 
Mast  cells,  119 
Matrix,  350 
Maturation,  25,  27,  311 
Maxillary  arch,  139 
Meatus,  auditory,  437 
Meckel's  diverticulum,  194 
Median  raphe,  397 
Medulla,  foramen  cecum  of,  389 

of  kidney,  260 

pyramids  of,  391 
Medullary  rays  of  kidney,  261 

sheath,  99,  101 

substance  of  cerebrum,  406 
Medullated  nerve  fibers,  99 
Meibomian  glands,  433 
Meissner's  corpuscles,  366 

plexus,  190,  206 
Melanin,  68 
Melanotic  sarcoma,  73 
Melting-point  of  paraffin,  460 
M'embrana  basilaris,  445 

cochlea,  446 

eboris,  158 

tectoria,  450 
Meninges  of  brain,  385 

of  cord,  372 
Menstruation,  305,  324 
Mesial  olivary  nucleus,  391 
Mesoblastic  somites,  33 
Mesoderm,  31 
Mesonephros,  258,  259 
Metanephros,  259 
Metaphase,  42 
Microsomes,  36 
Middle  ear,  438 


Milk  sinus,  333 
Mitosis,  40 

chromosomes  in,  40 

reduction,  27,  281 

somatic,  27 

Mixed  lateral  bundle,  318 
Modiolus,  444 

Molecular  layer  of  cerebrum,  403 
Moll's  glands,  433 
Monads,  283 
Monaster,  41 

Montgomery's  glands,  335 
Morgagni's  hydatid,  287 
Morula  stage,  29 
Mossy  cells,  104 

fibers,  391 
Mother  skein,  41 
Motor  decussation,  318,  389,  391 

nerve  endings,  361 
Moulting,  348 

Mounting  tissues  on  block,  459 
Mouth,  136 
Mucigen,  210 
Mucous  coat  of  small  intestine, 

194 
of  stomach,  185 

membrane,  defined,  59 
of  larynx,  233 
of  trachea,  242 

tissue,  67 
Muller's  fluid,  474 
Multipolar  cells,  98 
Mumps,  209 
Muscle,  85 

anisotropic,  90 

blood-supply  of,  92 

cardiac,  87 

ciliary,  420 

Cohnheim's  fields,  89 

endomysium,  88 

end-plate,  361 

epimysium,  88 

fasciculi  of,  88 

general  considerations,  93 

Hensen's  median  disc,  90,  91 

involuntary,  distribution  of,  86 

isotropic,  90 

Krause's  membrane,  90 

myoma,  93 

nerve-supply,  92,  93 

non-striated,   peripheral  nerve 
terminations  in,  362 


INDEX 


Muscle  of  accommodation,  420 

of  skin,  342 

perirrfysium,  88 

red,  92 

sarcolemma,  89 

sarcomere,  91 

sarcoplasm,  89 

sarcostyle,  86,  89 

sarcous  element,  91 

spindle,  370 

striated,  peripheral  nerve  ter- 
minations in,  361 

voluntary,  88 

distribution  of,  93 

white,  91,  92 

Muscular  layer   of   small   intes- 
tine, 200 
of  stomach,  190 
of  uterus,  322 

tissue,  85 
Myelocytes,  122 
Myeloplaxes,  122 
Myocardium,  circulatory,  108 
Myoma,  93 
Myotomes,  33 
Myxedema,  237 


NAIL  leaves,  351 
Nails,  349 

Nasofrontal  process,  140 
Nerve,  auditory,  450 
cells,  bipolar,  97 

of  posterior  horn,  375 
unipolar,  96 

endings,  free  sensory,  364 
motor,  361 
sensory,  363 
fibers,  99 

medullated,  99 
non-medullary,  103 
plexus,  96 
supply    of    alimentary    canal, 

206 

of  muscles,  92,  93 
of  teeth,  167 
of  tongue,  1 80 

terminations,  peripheral,  361 
in  non-striated  muscle,  362 
in  striated  muscle  361 
Nerves  of  kidney,  269 
of  liver,  229 


Nerves  of  lungs,  252 
of  mammary  gland,  335 
of  suprarenal  bodies,  256 
of  testicle,  289 
of  uterus,  323 
spinal,  374 

Nervous  system,  central,  blood- 
vessels of,  409 
tissue,  94 

axis  cylinder,  95,  99 
bipolar,  nerve  cells,  97 
classification  of,  96 
collaterals,  95 
dendrite,  96 
endoneurium,  104 
epineurium,  104 
exolemma,  101 
fibrils,  99,  100 
funiculus  of,  104 
ganglia,  96 

general  considerations,  106 
implantation  cone,  101 
medullary  sheath,  99,  101 
medullated  nerve  fibers,  99 
multipolar  cells,  98 
nerve  fibers,  99 
plexus,  96 
trunk,  104 
neuroma,  106 
neuron,  94 

theory,  107 
neuroplasm,  101 
neuropodia,  104 
node  of  Ranvier,  103 
non-medullary  nerve  fibers, 

103 

perineurium,  104 
Schmidt-Lantermann    seg- 
ments, 103 
spinal  ganglion,  97 
unipolar  nerve  cells,  96 
Net  knobs,  nuclear,  40 
Neumann's  sheaths,  156 
Neural  canal,  33 

groove,  371 
Neuroglia,  104,  406 
Neuroma,  106 
Neuromere,  384 
Neuron,  94 

theory,  107 
Neuroplasm,  101 
Neuropodia,  104 


INDEX 


489 


Neutrophiles,  119 

Nipple,  331 

Nitric  acid,  473 

Nitrogen,  19 

Nodes,  lymph,  function  of,  133 

Ranvier's,  103 

solitary  lymph,  197 
Nodules,  agminated  lymph,  198 
Nuclear  membrane,  473 

sap,  38 

Nuclei  pontis,  397 
Nucleolus,  38 
Nucleoplasm,  39 
Nucleus,  37 

arcuate,  391,  393 

cuneatus,  379 

Deiters',  382 

gracilis,  379 

mesial  olivary,  391 

solitary,  393 

Stilling's,  376 

ODONTOBLASTS,  156,  158 
Olfactory  organ,  449 
Olivary  body,  389,  393 

nucleus,  mesial,  391 
Olive,  superior,  397 
Omasum,  192,  193 
Ontogeny,  24 
Optic  papilla,  427 

vesicle,  primary,  411 

secondary,  411 
Ora  serrata,  427,  428 
Organ,  defined,  23,  25 

of  Corti,  447 
Osmic  acid,  472 
Ossification  of  bone,  83 
Osteoblasts,  84,  122,  165 
Osteoclasts,  84,  122,  165 
Osteogenetic  layer  of  bone,  80 
Os  uteri,  319 
Otoliths,  442 
Ovaries,  301 

tunica  albugmea,  303 
Ovulation,  25,  26,  305 
Ovules,  58 
Ovum,  23,  304,  308 
Oxygen,  19 

P  ACINI  AN  corpuscle,  369 
Palate,  142 


Palate,  cleft,  142 

Pal-Weigert  stain,  477 

Pancreas,  212 

centro-acinal  cells  of,  214,  215 
zymogen  granules  of,  214 

Papilla  of  hair,  348 
of  tongue,  175 

circumvallate,  176 
filiform,  175 
foliate,  179 
fungiform,  175,  176 
optic,  427 

Paradidymis,  287 

Paraffin  imbedding,  460 
advantages  of,  462 
disadvantages  of,  462 
melting-point  of,  460 
sections,  staining  of,  463 
solidification  of,  461 

Paralinin,  38 

Paraplasm,  36 

Parathyroids,  238 

Parietal  cells  of  salivary  glands, 
210 

Paroophoron,  317 

Parotid  glands,  99,  101 

Parotitis,  209 

Parovarium,  317 

Pars  ciliaris  retinae,  420 

Patches,  Peyer's,  129,  198 

Peduncle,    inferior,    of    cerebel- 
lum, 388 

Pelvis  of  kidney,  260 

Penis,  289 

glands  of,  289,  290,  292 

Pepsin,  1 88 

Pepsinogen,  188 

Perichondrion,  75 

Peridental  membrane,  161 

Perimysium,  88 

Perineurium,  104 

Periosteum,  80 

Peripheral    nerve    terminations, 

361 
in     non-striated     muscle, 

362 
in  striated  muscle,  361 

Peritoneum,  63 

Petit's  canal,  430 

Peyer's  patches,  129,  198 

Pharyngeal  tonsils,  180 

Pharynx,  180 


490 


INDEX 


Phytogeny,  24 
.  Pia  of  brain,  385 

of  spinal  cord,  373 
Picric  acid,  473 
Picrosulphuric  acid,  473 
Pigment  cells,  67 
Pigmentation,  73 
Placenta,  328 
Plasma  cells,  69 
Platelets,  blood,  119 
Pleura,  63,  243 
Pleurodont  dentition,  169 
Plexus,  Auerbach's,  190,  206 

Meissner's,  190,  206 

nerve,  96 

Podophyllous  tissue,  353 
Poisoning,  blood-,  134 
Polar  bodies,  26,  311 

rays,  42 
Polymorphic  cells  of   cerebrum, 

405 

Polynuclear  cells,  119 
Pons,  394 

gray  matter  of,  396 

trapezium  of,  396 

white  matter  of,  396 
Portal  canal,  220 
Posterior    gray    commissure    of 
cord,  375 

horn  of  cord,  375 

longitudinal  bundle,  393,  396 

root-fibers,  termination  of,  380 
Potassium  bichromate  and  for- 
malin, 475 
Pregnancy,  327 
Preparation  of  material,  456 
Preparing  tissue,  review  of,  464 
Prepuce,  290 
Prickle  cells,  341 
Processus  reticularis,  376 
Pronephros,  258 
Pronucleus,  27 
Prophase,  41 
Prostate  gland,  297 
Prostatic  sinus,  293 
Protoplasm,  17,  35 

elements  yielded  by,  19 

metamorphosis  of,  20 

properties  of,  18,  20 

theory,  35 
Pupil,  421 
Purkinje's  cells,  400 


Pyramidal  cells  of  cerebrum,  405 

tract,  crossed,  381 

direct,  383 
Pyramids,  Malpighian,  260 

of  Ferrein,  261 

of  medulla,  391 

RANVIER'S  node,  103 
Raphe,  median,  397 
Receptaculum  chyli,  126 
Red  blood-corpuscles,  116 
crenated,  117 

muscle,  92 

Reduction  mitosis,  27,  281 
Refractory  media  of  eye,  428 
Regeneration  of  bone,  83 
Reissner's  membrane,  446 
Renal  sinus,  260 
Reproductive  organs  in  female, 

305 

Respiratory  bronchi,  244 
Restiform  body,  388 
Rete  testis,  278,  284 
Reticular  connective  tissue,  71 
Reticulum,  192,  193 
Retina,  421 
Retzius'  lines,  149 
Review  of  preparing  tissue,  464 
Rods  of  Corti,  448 
Rolando's  substantia  gelatinosa, 

375,  39i 
Rouleaux,  116 
Rufini  corpuscles,  354 
Rumen,  192 
Ruminants,  stomach  in,  192 

SACCUL^  of  large  intestine,  200, 

201 
Sacculus,  440—442 

endolymphaticus,  441 
Salivary  glands,  207 
accessory,  211 
parietal  cells  of,  210 
Santorini's  duct,  214 
Sap,  nuclear,  38 
Sarcode,  85 
Sarcolemma,  89 
Sarcoma,  72 

melanotic,  73 
Sarcomere,  91 


INDEX 


491 


Sarcoplasm,  89 

Sarcostyle,  86,  89 

Sarcous  element  of  muscle,  91 

Sartoli's  column,  277 

Scala  tympani,  446 

vestibuli,  446 
Schlemm's  canal,  415 
Schmidt-Iyantermann    segments, 

103 

Sclera,  151 
Sebaceous  cysts,  359 

glands,  359 
Sebum,  359 
Secondary  dentin,  157 
Secreting  membranes,  62 
Sections,  cutting,  462 
Segmentation,  28 
Segments,  Schmidt-Lantermann, 

103 

Semen,  288 

Semicircular  canals,  440,  443 
Seminal  vesicles,  286 
Sensitive  lamina,  351,  353 
Sensory  decussation,  390 

nerve  endings,  363 

free,  364 
Serous   coat   of  small   intestine, 

200 
of  stomach,  190 

membrane,  defined,  60 
Sex,  determination  of,  48,  283 

influences  affecting,  284 
Sharpey's  fibers,  80 

primary  areolae,  81 

secondary  areolae,  82 
Sheaths  of  Neumann,  156 
Sinus,  milk,  333 

pocularis,  293 

prostatic,  293 

renal,  260 
Skein,  daughter,  43 

mother,  41 
Skin,  337 

layers  of,  339 

muscle  of,  342 
Small  intestine,  194 

blood-supply  of,  203 
mucosa,  194 
muscular  layer,  200 
serosa,  200 
submucosa,  199 
Smegma,  290 


Sole  plates,  361 
Solidification  of  paraffin,  459 
Solitary  lymph-node,  128 

nucleus,  393 
Somatic  mitosis,  27 
Somatopleure,  31 
Somites,  mesoblastic,  33 
Spermatids,  278,  281 
Spermatoblasts,  278 
Spermatocytes,  278 
primary,  281 
secondary,  281,  282 
Spermatogenesis,  281,  282 
Spermatogonia,  277 
Spermatozoa,  58,  280 

influence  of,  on  sex  determina- 
tion, 284 
structure  of,  284 
Sphere,  attraction,  42 
Spider  cells,  102 
Spinal  cord,  371 

anterior     gray     commissure 

of,  375 
horn  of,  376 
arachnoid  of,  373 
blood-supply  of,  409 
cauda  equina,  371 
central  canal  of,  375 
cervical  enlargement,  371 
dura  of,  372 
filum  terminale,  371 
fissures  of,  373 
gray  matter  of,  375 
lateral  horn  of,  376 
lumbar  enlargement,  371 
membranes  of,  372 
meninges  of,  372 
origin  of,  33 
pia  of,  373 
posterior    gray    commissure 

of,  375 
horn  of,  375 
tracts  of,  379 

summary,  394 
white  matter  of,  376 
ganglion,  101 
nerves,  374 
Spindle  muscle,  370 
Spiral  ganglia,  450 
Spirem,  41 
Splanchnopleure,  31 
Spleen,  135 


492 


INDEX 


Spleen,  function  of,  138 

ampulla  of  Thoma  of,  137 

in  typhoid  fever,  139 

Malpighian  corpuscle  of,  136 
Spongioplasm,  36,  39 
Staining  celloidin  sections,  462 

paraffin  sections,  463 
Stains,  475 

anilin,  477 

Pal-Weigert,  477 
Stellate  cells  of  cerebellum,  399 

of  Kupffer,  229 
Stenson's  duct,  207 
Stigmata,  68 

of  blood-vessels,  116 
Stilling's  nucleus,  376 
Stomach,  184 

blood-supply  of,  203 

crypts  of,  1 86 

glands  of,  187 

in  ruminants,  192 

mucosa,  185 

muscular  layer,  ^90 

serosa,  190 

submucosa,  189 
Stomata,  64 

of  blood-vessels,  116 
Stomodeum,  138 
Stratum    granulosum    of    ovum, 

306 
of  skin,  340 

lucidum,  340 
Striae  acusticse,  388 
Striated  muscle,  peripheral  nerve 

terminations  in,  361 
Stroma,  blood,  116 
Subarachnoid  space,  386 
Subendothelium  of  arteries,  109, 

up 

Sublingual  gland,  209 
Submaxillary  gland,  211 
Submucous  coat  of  small  intes- 
tine, 199 
of  stomach,  189 
Substantia  gelatinosa  of  Rolando, 

377,  39i 

Sulphur,  19 

Superior  olive,  397 

Supporting  tissue,  64 

Suprarenal  glands,  62,  253 
blood-vessels  of,  255 
clinical  features,  257 


Suprarenal  glands,  nerves  of,  256 

structure  of,  254 
Sweat  glands,  356 
Sympathetic  system,  105 
Synapsis  of  chromosomes,  281 
Syncytium,  330 
System,  denned,  23 


TACTILE  cells,  365 

hairs,  346 
Taeniae  coli,  200 
Tarsal  glands,  433 

plates,  434 
Taste  buds,  177 
Teasing,  456 
Teeth,  143 

attachment  of,  168 

blood-supply  of,  166 

cementum,  159 

dentin,  155 

development  of,  170 

enamel,  147 

rods,  directions  of,  150 

lines  of  Retzius,  149 

nerve  supply,  167 

secondary  dentin,  157 

structure  of,  147 
Teichman's  crystals,  120 
Telophase,  43 
Tendon  spindle,  369 , 
Tenon's  capsule,  415 
Tentorium,  385 
Testes,    interstitial   elements  of, 

278,  279 
Testicle,  383 

excretory  ducts  of,  284 

function  of,  279 

interstitial  cells  of,  62 

lymphatics  of,  289 

nerves  of,  289 

structure  of,  277 

vessels  and  nerves,  237 
Tetrads,  282 
Theca,  306 

Thecodont  dentition,  169 
Thoma,  ampullae  of,  133 
Thoracic  lymph  duct,  1 26 
Thymus  gland,  129 
function  of,  133 
Thyroglossus  duct,  235 
Thyroid  gland,  62,  235 


INDEX 


493 


Thyroid  gland,  structure  of,  236 

vessels  and  nerves  of,  237 
Thyroidima,  237 
Tissues,  classified,  187 

defined,  23,  25 
Tomes'  granular  layer,  156 
Tongue,  172 

blood-supply  of,  180 

foramen  cecum  of,  174 

glands;  of,  179 

nerve  supply  of,  180 

papillae  of,  175 
circumvallate,  176 
filiform,  175 
foliate,  179 
fungiform,  175,  176 
Tonsil,  181 

pharyngeal,  180 
Trachea,  239 

cartilage  of,  240 

mucous  membrane  of,  242 

structure  of,  239 
Tracts  of  cord,  summary,  384 
Trapezium  of  pons,  396 
Trigone  of  bladder,  272 
Trigonum  hypoglossi,  388 

vagi,  388 

Tubular  casts  of  kidney,  265 
Tubules  of  kidney,  262 
Tubuli  recti,  278,  283 

adventitia  of  artery,  109,  1 1 1 

albuginea,'  276,  303 

externa  of  eye,  414 

intima  of  artery,  109 

media  of  artery,  109,  in 

vaginalis,  274,  275 

vasculosa,  276 
Tympanic  cavity,  438 

membrane,  434 
Typhlosole,  196 
Typhoid  fever,  spleen  in,  135 
Tyson's  glands,  290 

UNICELLULAR  glands,  57>  5 8 
Unipolar  nerve  cells,  96 
Ureters,  269 

function  of,  271 

structure  of,  269 
Urethra  in  female,  94 

in  male,  292 
Urinary  organs,  253 


Uterus,  317 

masculine,  293 

muscular  layer,  322 

structure  of,  321 

vessels  and  nerves  of,  323 
Utriculus,  440 


VACUOLES,  39 

Valvulae  conniventes,  195 

Vas  deferens,  285 

structure  of,  286 
Vasa  efferentia,  284 

vasorum,  122,  124 
Vascular  laminae,  351,  353 
Veins,  113 

Vermiform  appendix,  202 
Vernix  caseosa,  339 
Verumontanum,  293 
Vestibule,  440 
Villi,  chor ionic,  329 

of  small  intestine,  196 
Visceral  arches,  138 
Vitelline  membrane,  310 
Vitellus,  309 
Vitreous  humor,  412,  430 

membrane  of,  419 
Vocal  cords,  234 
Volkmann's  canals,  78 
Voluntary  muscle,  88 
distribution  of,  93 


WALDEYER'S  central  cell  column, 

376 

Wandering  cells,  69,  119 
Washing  tissues,  458 
Weigert-Pal  stain,  477 
Weil,  layer  of,  159 
Wens,  360 
Wharton's  duct,  70,  211 

jelly,  67,  331 
White  blood-corpuscles,  118 

fibrous  cartilage,  76 
connective  tissue,  70 

matter  of  pons,  395 
of  spinal  cord,  376 

muscle,  91,  92 
Winslow's  foramen,  219 
Wirsung's  duct,  213 
Wolffian  body,  258 

duct,  258 


494 


INDEX 


YEU,OW  elastic  connective  tissue, 


ZELLKNOTEN,  330 
Zenker's  fluid,  474 


Zona  pellucida,  308 

radiata,  308 

reticularis,  375 

terminalis,  375 
Zymogen,  209 

granules  of  pancreas,  214 


UNIVERSITY    OF   CALIFORNIA 
BRANCH    OF    THE    COLLEGE    OF    AGRICULTURE 

THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


^s    SI&& 

;^   ' 
gEC^      W*« 

/IP 

Wr  27  "40    u  " 

D  LIBRARY 

APR  tow  DUE  JUN5 


1  3 


8EP20'50 


3rn-9,'30 


CLM5SI 
~ 


LIBRARY,  BRANCH 


f-S? 

OF  THE  COL 


COLLEGE  OF  AGRICULTURE,  DAVIS 


